TEPCO Fukushima Daini Nuclear Power Station
Research on the status of response to the Tohoku-Pacific Ocean
Earthquake and Tsunami and Lessons learned therefrom(Proposals)

October 2012

Japan Nuclear Safety InstituteTable of contents
Introduction......................................................................................................................2
Overview of Fukushima Daini Nuclear Power Station .................................................4
2.1 Overall Layout...........................................................................................................4
2.2 System Configuration ..............................................................................................5
2.3 Power Supply System ..............................................................................................7
2.4 Severe Accident Countermeasures; Accident Management ................................9
3. Overview of the tsunami caused by the Tohoku-Pacific Ocean Earthquake ........... 11
3.1 Overview of the Earthquake and the tsunami...................................................... 11
3.2 Results of observation at Fukushima Daini .........................................................15
3.3 Data on the earthquake and subsequent tsunami...............................................16
3.4 Damage of Equipment............................................................................................173.4.1 Damage by the earthquake .............................................................................17
3.4.2 Damage by the tsunami ..................................................................................19
4. Response to the accident at Fukushima Daini ...........................................................23
4.1 Response status from the time of the earthquake and tsunami until restorationand cold shutdown ................................................................................................29
4.2 Emergency response situation .............................................................................30
4.2.1 Immediately after the earthquake...................................................................30
4.2.2 Immediately after the arrival of the tsunami..................................................33
4.2.3 Responses toward restoration after the arrival of the tsunami...................34
4.2.3.1
Overview of the power plant ....................................................................34
4.2.3.2
Situation of Fukushima Daini Unit 1. ......................................................38
4.2.3.3
Situation of Fukushima Daini Unit 2. ......................................................39
4.2.3.4
Situation of Fukushima Daini Unit 3. ......................................................41
4.2.3.5
Situation of Fukushima Daini Unit 4 .......................................................42
4.3 Cooling of spent fuel pool of Fukushima Daini ...................................................44
5. Analysis of accident response.....................................................................................45
5.1 Purpose of the analysis of accident response ....................................................45
5.2 Concept of analysis................................................................................................45
5.3 Specific analysis procedures ................................................................................46
5.4 Important lessons obtained from the analysis ....................................................59
6. Emergency response as seen from the viewpoint of the human factor ..................61
7. Lessons ..........................................................................................................................64
7.1 Organization, management, communication .......................................................64
7.2 Advance preparation (equipment, manual, training)...........................................65
7.3 Initial response in the accident .............................................................................66
7.4 Additional measures ..............................................................................................67
8. Conclusion .....................................................................................................................68
Attachment Recommended Actions for the Emergency Response by
Equipments/Materials Reinforcement ................................................................................69
1.
2.

1. Introduction.
For everyone associated with nuclear power, March 11, 2011 has become a day which will
never be forgotten. This day will be long remembered by those in the nuclear industry for
years to come.
Even now, a large number of people still have to endure stressful lives as refugees. If weconsider the length of time as well as the size and range of the damage, we will profoundly
recognize the enormity of the damage of the nuclear disaster.
Meanwhile, TEPCO’s Fukushima Daiichi Nuclear Power Station (hereinafter referred to as"Fukushima Daiichi"), is in the middle of a restoration process for accident convergence inaccordance with the roadmap, and the situation of the power plant may be considered to havesubsided substantially.
National agencies, local governments, industries, academia, volunteer groups and local
residents are making efforts for decontamination and other tasks toward the restoration of theregion, and as a result, some areas have managed to relax access restriction. Although there
were the most stringent controls on the shipment of food from the outset of the accident,
restrictions have been lessened little by little but it is still necessary to continue the constantmonitoring.
The level of radiation to which residents are exposed is regulated based on knowledge of thedose rate obtained from historical data, including survivors of the atomic bombs dropped on
Hiroshima and Nagasaki, but this is not considered to provide clarity in indicating thelate-onset effects of radiation exposure, and we do not think that a situation will develop in
which there will be significant increase in cancer incidence due to radioactive materials. The
national government will continuously monitor the health of residents in the future.
Extensive validations have been performed about the Fukushima Daiichi accident, and many
reports have been published. Our Institute has also issued a proposal with the cooperation of
TEPCO and manufacturers which was published at the end of last October as a statementfrom the industry. It focuses primarily on the hardware to combat tsunami to prevent accidents
from expanding. We believe that the expansion of this accident and the massive release ofradioactive materials into the environment could have been prevented if appropriate
measures had been taken.
Dr. Hatamura, Chairman of the Accident Investigation Committee of the government, stated ina special NHK program that "this accident at Fukushima Daiichi could have been averted if
proper and adequate preparations had been in place.”
There is an ongoing national discussion of what to do about the energy supply in the future;
we think that inexpensive natural energy is not sufficient at present, and will not be secure in
the future, and that considering big problems such as energy security, global warming, andremaining internationally competitive (the hollowing out of domestic industry), it would beunrealistic to eliminate all nuclear power entirely.
Before the accident at Fukushima Daiichi, the Democratic Party, the current ruling party,
promised the international community a 25% reduction of CO2 emissions and was planning toincrease the proportion of nuclear power to 40%. How we can achieve our international
commitment to CO2 reduction without nuclear power? And how long we can continue to pay
as much as three trillion yen each year to operate thermal power plants instead of nuclear
power plants, in addition to buying fossil fuels? In view of these difficult issues, we think thatthe realistic option for the time being is to continue using nuclear power while improving its
safety.
Following the industry report analyzing the Fukushima Daiichi accident, our Institute decided2

to validate the post-tsunami response situation at the Fukushima Daini Nuclear Power Station(hereinafter referred to as "Fukushima Daini") which successfully led the station toconvergence, both from a technical perspective and from the viewpoint of a third party, with
the intent of gathering lessons in order to enhance the accident response capability of nuclear
power plants and contribute to the improvement of safety.
Details of the sequence of events and responses to the Fukushima Daini accident havealready been fully described in the accident analysis reports such as by the Government andby TEPCO. Therefore, this report is dedicated to summarizing the overview of the sequenceof events and accident responses, and it is intended to pick out good practices which include
lessons for the future. In compiling these lessons, we tried to make our recommendations as
specific as possible by describing the necessary level of preparedness based on the actual
accident responses.
We hope that the lessons of this report will be utilized when nuclear power plants in Japan andthroughout the world consider possible measures against accidents.
As stated above, our report on the Fukushima Daiichi accident, which primarily summarizes
the hardware and recommends various measures, is available at the Japan Nuclear Safety
Institute’s website (former Japan Nuclear Technology Institute). Please visit the page.
In this report, we basically excluded the analysis of the activities of the central and local
governments and confined our analysis to gathering lessons about aspects to which electricutility companies should be able to respond.

32. Overview of Fukushima Daini Nuclear Power Station
2.1 Overall Layout
Fukushima Daini is located in the towns of Naraha and Tomioka in Futaba-gun, Fukushima
Prefecture, about 12 km south of Fukushima Daiichi, facing the Pacific Ocean to the east.
The site is approximately 147 million m2 and its shape is almost square.
At present, four units of boiling water reactors have been installed and are arranged in theorder of No. 1, 2, 3, and 4 from the south. The generating capacity of these units is 1,100
MW each, making for a total installed capacity of power generation of 4,400 MW.
When the recent disaster occurred, all units 1 to 4 were in operation at the rated thermal
output.
One central control room controls two units of reactors in a twin plant design: Units 1 and 2
make up one pair and Units 3 and 4 another.

Waste Treatment
Building
Unit 4

Unit 3

Unit 2Main Office
Building

Unit 1

Important Seismic
Isolation Building

Reactor Building
Turbine Building
Seawater Heat
Exchanger Building

Location

Unit

Start of
Operation

Naraha
town

1
2
3
4

S57.4
S59.2
S60.6
S62.8

Tomiokatown

Reactor

BWR5

Type
Pressure VesselMark IIMark II R
Advanced

Output(MW)Situation when
event happened

1,100
1,100
1,100
1,100

In operation at the
rated thermal
outputFig 2.1 Overall Layout of Power Stations4

2.2 System Configuration
The system configuration of each unit of Fukushima Daini is as shown in Fig 2.2.
The role of each system is as follows:• Reactor Core Isolation Cooling System (RCIC)In the event that the main condenser is no longer available for any reason, such as
closure of the main steam isolation valve during normal operation, steam from thereactor will activate the turbine drive pump to inject the water in the condensate storagetank (referred to as "CST" below) into the reactor, and reduce the pressure by removing
the decay heat of the fuel. The system also works as an emergency water injection
pump in case of the failure of the water supply system, etc., and maintains the waterlevel in the reactor.
• Residual Heat Removal System (RHR)
After shutting down the reactor, the system will cool the coolant (remove the decay heatof the fuel) using pumps and the heat exchangers, or maintain the level of reactor waterby injecting cooling water in case of an emergency (part of ECCS). The system has theability to bring the reactor to cold shutdown and has five modes of operation: reactor
shutdown cooling mode, low-pressure injection mode (ECCS), containment spray mode,pressure suppression chamber cooling mode, and emergency heat load mode.
• Emergency Core Cooling System (ECCS)
The system consists of four subsystems: low pressure core spray system (LPCS), lowpressure water injection system, high pressure core spray system (HPCS) andautomatic depressurization system. In the case that a loss-of-coolant accident (LOCA)
has occurred due to a piping break in the reactor coolant pressure boundary, such as
the primary loop recirculation system piping, the system will remove the residual heatand the decay heat of the fuel in the reactor core, preventing the fuel cladding tube frombeing damaged by the fuel overheating, and consequently, minimize and suppress thewater-zirconium reaction to a negligible extent.
• Standby Liquid Control System (SLC)
If and when control rod insertion becomes impossible for any reason during reactor
operation, the system will inject a neutron-absorbing boric acid solution from the bottomof the reactor core as a backup for the control rod to stop the nuclear reaction.

5

Water Pump
(Turbine driven,
2 units)

RCIC Pump

Main Turbine
Condenser

Water Pump
Condensate Pump
(Motor driven, (High Pressure, 3 units)
2 units) (Low Pressure, 3 units)

CST, from
Suppression Poolto Suppression
Pool

Circulating Water
Pump (3 units)from MUWC to RHR (B) Pump
Pump

to RHR

HPCS Pump

to RCIC
RHR (A) Pump

SLC Tank

Sea

Condensate Storage
Tank (CST)CRD Pump,
2 units

from CSTMUWC Pump *2

RHR (C)Pump

to HPCS RCIC CRD

RHR (B)
Pump
from PLR (A)from CSTLPCS Pump

SLC Pump,
2 units*1 PLR (A) in Unit1, PLR (B) in Unit 2*2 Pump three units in Unit 1, two units in Unit 2

Fig 2.2-1 System configuration of Fukushima Daini Unit 1 and 2

Water Pump
(Turbine driven,
2 units)

RCIC Pump

Main Turbine
Condenser

Water Pump
(Motor driven,
2 units)

CST, from CST, S/P
to Suppression
Pool

Condensate Pump
(3 units)
Circulating Water
Pump (3 units)
Seafrom MUWC to RHR (B) Pump
Pump

to RHR

HPCS Pump

to RCIC
RHR (A) Pump

SLC Tank

Condensate Storage
Tank (CST)from CSTCRD Pump,
2 units

from CSTRHR (C)Pump
RHR (B)
Pump
from PLR (B)SLC Pump,
2 units

LPCS Pump

Fig 2.2-2 System configuration of Fukushima Daini Unit 3 and 4

6

MUWC Pump(3 units)
to HPCS RCIC CRD

2.3 Power Supply System
The electricity generated by these units is transmitted via two 500 kV lines (Tomioka Line)to the power grid. The transmission capacity of one Tomioka line is sufficient for all theelectricity generated at Fukushima Daini, and therefore the power plant can continue full
output generation even in the case of failure in one transmission line.
The power plant receives the power for starting and shutting down the reactor via two
Tomioka Lines as the main circuits, or via two 66 kV lines (Iwaido Line) as the backup
circuit.
In the event of a blackout of these two Tomioka Lines and two Iwaido Lines, the emergency
electricity to safely shut down the reactor is powered by emergency diesel generators (D/G)
and D/G in the high pressure core spray system (HPCS).
The Iwaido and Tomioka lines are shared by all units.

7500 kVTomioka Line

Series 1

66 kV

Series 2

Iwaido Line

Series 1 Series 2

Circuit Breaker ON
Circuit Breaker OFF (Standby)
Charging

G

G

Unit 1

Unit 2

G

66 kV Electric
Boiler Switching
StationG

Unit 3 Unit 4

Startup Switching Station

High Voltage
Startup Transformer

Startup Transformer
1SA
6.9 kV M/C
1SA-1

Unit 1

Startup Transformer
1SB

6.9 kV M/C
1SA-2

6.9 kV M/C
1SB-1

Startup Transformer
3SA

6.9 kV M/C
1SB-2

6.9 kV M/C
3SA-1

Startup Transformer
3SB

6.9 kV M/C
3SA-2

6.9 kV M/C
3SB-1

6.9 kV M/C
3SB-2

Note

D/G(HPCS)

D/G(A)

D/G

D/G

*1

D/G(B)D/G*3*5

RHRS Pump (D)RHRS Pump (B)

RHRC Pump (D)RHRC Pump (B)

EECW Pump (B)RHR Pump (C)RHR Pump (B)

RHRS Pump (C)RHRS Pump (A)RHRC Pump (C)RHRC Pump (A)EECW Pump (A)HPCS Pump

HPCS Pump

RHR Pump (A)LPCS Pump

HPCS Pump

Note：※1,※3,※5 shall be replaced to read;
Replace to read
Unit 1 Unit 2 Unit 3 Unit 4
*1
*2
*7
*8
*3
*4
*9
*10
*5
*6
*11
*12

Fig 2.3-1 Power system diagram, skeleton diagram of emergency power system8

2.4 Severe Accident Countermeasures; Accident Management
Table 2.4 describes Fukushima Daini’s accident management.
Countermeasures are prepared to mitigate the effects in the event that the situation has
expanded to a severe accident.
Table 2.4 Established Severe Accident Countermeasures
Function
Reactor shut down

Water injection to reactor core andcontainment vessel

Heat removal from containment vessel

Support for safety functions

Severe Accident Countermeasures
Recirculation Pump Trip (RPT)
Alternate Rod Injection (ARI)
Alternate Water Injection(Water injection into reactor core/containment vesselby make-up water pump/fire extinguishing pump )Automatic Depressurization of reactor core.
(Additional interlock in ADS)
Alternate heat removal (Utilization of D/Wcooler/reactor coolant cleanup system)
Restoration of damaged equipment in the residual heatremoval system(Procedure)
Hardened Vent
Power sharing (accommodation of 480 V power fromthe adjacent plant)
Restoration of damaged equipment in the emergency
D/G(Procedure)

9Abbreviations: Reactor Pressure Vessel

RCIC: Reactor Core Isolation Cooling

LPCI: Low Pressure Coolant Injection

RHR: Residual Heat Removal

Diesel Driven
Pump

FP System

RPV

RCIR

Electric Pump
MUWC System

Filtered Water
Tank
FP System

LPCI Water
Injection

Electric Pump

RPV
MUWC
SystemRHR

D/W

Condensate
Storage Tank

Pedestal Water Injection

MUWC System
Suppression Pool
Boundary of System

RHR
System

Fig 2.4-1 Alternate Water Injection

Stack

Reactor Building
Exhaust Duct

Standby Gas Treatment
System (SGTS)
Rupture Disk
D/W
Suppression Pool

Inert Gas System(Containment
Vessel Boundary)

SGTS System

Fig 2.4-2 Hardened Vent

10

: Boundary of System

3. Overview of the tsunami caused by the Tohoku-Pacific Ocean Earthquake
3.1 Overview of the Earthquake and the tsunami
The Tohoku-Pacific Ocean Earthquake, which occurred on March 11, 2011, was the biggest
earthquake that has ever been observed in Japan in terms of the main shock. In thisearthquake, a maximum seismic intensity of 7 was observed in Kurihara City, Miyagi
Prefecture.
High tsunamis were observed on the coast of Pacific Ocean in Hokkaido, Tohoku, and the
Kanto region.
The focal region of this earthquake ranges from offshore Iwate Prefecture to offshore
Ibaraki prefecture, with a size of about 500 km in length and about 200 km in width. The
length of maximum slippage was estimated at more than 50 m.
In this earthquake, several large slippages were observed in the offshore of the southernpart of Sanriku near the trench, the northern part of Sanriku, and some areas off the coastof the Boso Peninsula near the trench, evidencing that multiple focal regions off the coastof central Sanriku, Miyagi, Fukushima, and Ibaraki concurrently slipped to generate amega-earthquake of magnitude 9.0 (the fourth largest ever observed in the world). The
Headquarters for Earthquake Research Promotion, a national center for the research andstudy of earthquakes and tsunamis, had been monitoring and evaluating the ground motionof individual regions with case records in the past, but had not assumed for the condition of
quakes occurring in all of these areas in conjunction. The Expert Committee of the Central
Disaster Management Council has also asserted that this enormous earthquake with amagnitude of 9.0 occurred with several source regions linking together in conjunction,
which could not have been assumed from the past few hundred years of our country’s
earthquake history.
The tsunami that occurred due to this earthquake and caused the most extreme
devastation along the Pacific Ocean coast in the northeastern region of Japan was amagnitude 9.1 on the tsunami scale, making it the fourth largest ever observed in the world
and the largest in Japan.

11

Earthquake off Sanriku, March 11, 2011 2:46 pm
Seismic Intensity Map

LegendSeismic
Intensity 7
Seismic
Intensity 6+
Seismic
Intensity 6Seismic
Intensity 5+
Seismic
Intensity 5Seismic
Intensity 4
Seismic
Intensity 3
Seismic
Intensity 2
Seismic
Intensity 1

Epicenter

Source: Japan Meteorological Agency(Earthquake off Sanriku, March 11, 2011 2:46 pm Seismic Intensity Map)

12

Seismic Source
Time Function

sec.
Starting point of bedrock destruction in
the main shock
Epicenter of M7+ shock after March 9
Epicenter of M5+ shock within 1 day
after main shock
Center of each small fault
Observation Point used in the analysis

Slippage (m)Contour Interval: 4 m

Source: Japan Meteorological Agency(March 2011 Earthquake and Volcanic Activity Monthly Report)
The tsunami is thought to have occurred due to the seabed almost directly above theepicenter rising by about 3 m. The maximum height of tsunami run up above sea level wasobserved at nearly 35 m in northern Miyako city. The height of the flooding in the northernpart of Miyako city was more than 25 m, and there were 58 km2 of flooded areas in Iwate,
327 km2 in Miyagi, 112 km2 in Fukushima, and 23 km2 in Ibaraki.

13

[ Legend ]Evidence of Tsunami

Offshore Tohoku Flood
HeightOffshore Tohoku
Run-up Height

AomoriPrefecture
Hachinohe

Miyako
Iwate
Prefecture
Rikuzentakata

Sendai

MiyagiPrefecture(Source)• 2011 Tohoku-Pacific
Ocean Earthquake
Flood Height andRun-up Height :Preliminary Figures by"Joint Investigation
Group onTohoku-Pacific Ocean
Earthquake andTsunami" (May 9, 2011)
Remarks: Based on the
Data with Reliability
Level A (Highly reliablewith clear trace andminimal measurement
error) obtained within anarea of 200 m from theshoreline.

Fukushima
Prefecture

IbarakiPrefecture

Flood Height and Run-up Height
Flood Height

Embankment

Run-up Height

Flood Height:
Run-up Height:

Sea level at the time oftsunami arrival
Tokyo Peil: Mean sea
level at Tokyo Bay (T.P.)

Height from the sea level at the time of arrival of thetsunami to the traces of tsunami inundation
Height from the sea level at the time of arrival of thetsunami to the traces of tsunami run-up.

Source: Excerpt from the 1st Meeting Material by The Investigation Committee on theCountermeasures learned as Lessons from the Tohoku-Pacific Ocean Earthquake
As of July 31, 2012, the damage caused by the earthquake and the tsunami is enormous:
15,867 dead, 2,903 missing, 130,445 buildings totally destroyed, and 264,110 buildings
partially destroyed.

14

3.2 Results of observation at Fukushima Daini
The observed values of ground motion at the foundation of the reactor building (the lowest
basement floor) of Fukushima Daini was below the maximum acceleration of design
earthquake ground motion Ss (the maximum acceleration observed was 305 Gal on the B2
floor of the Unit 1 reactor building), and therefore this ground motion can be considered to
be within the expected range of the seismic safety evaluation of the equipment.

Acceleration (Gal)

Acceleration (Gal)Furthermore, using the recorded values of ground motion at the free field obtained during
the earthquake, a soil structure model was identified for the strip analysis. As a result,ground motion of the strip analysis proved to be generally at the same level as actual
observations, although the calculated values exceeded the design earthquake groundmotion Ss in some of the periodic bands.
Recorded Measurement
Basic Seismic Movement Ss-1
Basic Seismic Movement Ss-2
Basic Seismic Movement Ss-3

Time (sec.)

Fig. 3.2-1-1 Time History of Acceleration on the Ground
Level of Reactor Building, Unit 1 (NS Direction)

Cycle (sec.)

Acceleration (Gal)

Acceleration (Gal)Fig. 3.2-2-1 Response Spectrum
on the Ground Level of Reactor
Building, Unit 1 (NS Direction)
Recorded Measurement
Basic Seismic Movement Ss-1
Basic Seismic Movement Ss-2
Basic Seismic Movement Ss-3

Time (sec.)
Cycle (sec.)

Fig. 3.2-2-2 Response Spectrum
on the Ground Level of Reactor
Building, Unit 2 (NS Direction)

Acceleration (Gal)

Acceleration (Gal)Fig. 3.2-1-2 Time History of Acceleration on the Ground
Level of Reactor Building, Unit 2 (NS Direction)

Recorded Measurement
Basic Seismic Movement Ss-1
Basic Seismic Movement Ss-2
Basic Seismic Movement Ss-3

Time (sec.)
Cycle (sec.)

Fig. 3.2-2-3 Response Spectrum
on the Ground Level of Reactor
Building, Unit 3 (NS Direction)

Acceleration (Gal)

Acceleration (Gal)Fig. 3.2-1-3 Time History of Acceleration on the Ground
Level of Reactor Building, Unit 3 (NS Direction)

Recorded Measurement
Basic Seismic Movement Ss-1
Basic Seismic Movement Ss-2
Basic Seismic Movement Ss-3

Time (sec.)

Fig. 3.2-1-4 Time History of Acceleration on the Ground
Level of Reactor Building, Unit 4 (NS Direction)

Cycle (sec.)

Fig. 3.2-2-4 Response Spectrum
on the Ground Level of Reactor
Building, Unit 4 (NS Direction)

Exemplification of larger horizontal direction in table153.3 Data on the earthquake and subsequent tsunami(1) Date and time of occurrence
March 11, 2011, 2:46 pm(2) Epicenter
Off the coast of Sanriku(38.1 N/142.9 E, 130 km ESE of Oshika Peninsula, focal depth 24 km)(3) Magnitude
9.0(4) Peak ground acceleration
305 Gal at B2 floor of the Unit 1 reactor building (Vertical)(5) Distance from Fukushima Daini
183km to epicenter, 185 km to hypocenter(6) Data on tsunamiaInundation height(a) Seaside area (Ground height at base level of Onahama Port Construction site(hereinafter O.P.) + 4 m)•
About +7 m*1 (flood depth about 3 m)
*1) South side of Unit 1 seawater heat exchanger building. Highest point(b) Main building*2 area (Ground height O.P. + 12 m)*2 Reactor building and Turbine
building•
O.P. about +12~+14.5 m*2 (flood depth less than 2.5 m)*2) Between the area south of Unit 1 Main building and the important seismic isolationbuilding.
Locally O.P. about+15~+16 m (flood depth about 3-4 m)b

Flooded area
The flooded area extended across the entire seaside area, but no entry of tsunami
seawater into the main building area beyond the slope from the seaside area wasobserved. The tsunami run up was mostly from the southeast side of the main building
area toward the road leading to the important seismic isolation building. As a result,flooding was limited only to the area surrounding the Unit 1 and 2 buildings and thesouth side of the Unit 3 building (no flooding around the Unit 4 building).

(7) Arrival of the first wave of the tsunami
March 11, 2011 3:22 pm Visual sighting)16

3.4 Damage of Equipment
3.4.1 Damage by the earthquake
The external power supply of Fukushima Daini consists of a total of four lines: 500 kV ofTomioka 1L and 2L and 66kV of Iwaido 1L and 2L, all from the Shin Fukushima
substation. On the day of the earthquake, however, Iwaido 1L was out of service forinspection and only three lines were available.
After the earthquake, Tomioka 2L went out of service at around 2:48 pm on March 11 dueto damage to the breakers at the Shin Fukushima substation. After the earthquake,
patrol inspection of facilities found damage at the arrester of Iwaido 2L, so after
confirming that Tomioka 1L was continuously receiving all the power necessary for thestation, Iwaido 2L was put out of service for restoration works in order to prevent thedamage from spreading further.
As a result, after the earthquake, the external power supply was only available from asingle line for the time being. However, Iwaido 2L resumed service at 1:38 pm on thenext day, March 12, and Iwaido 1L was also revived at 5:15 am on March 13 after
temporary restoration, giving the receiving configuration three lines.
Maintaining the external power through this single transmission line made it possible tosupply power to the available facilities, contributing a great deal to preventing the spreadof the accident, and led to early convergence. All the equipment such as circuit breakers,
etc. at the substation and switching stations has basically the same specifications as at
Fukushima Daiichi.

17

Shin Fukushima Transformer Substation

Under
construction
Suspension of Electric
Cable (Out of Service)

Iwaido Line Line 1L

Iwaido Line Series 1,
Suspended for repair works

Unit 1

Unit 2

Unit 3

Unit 4

Switching Station
for Auxiliary Boiler

66 kV Startup Switching Station

SwitchingStation forTransformer
Start-up

Ordinary High Voltage Power Panel(M/C)

Ordinary High Voltage Power Panel(M/C)
Emergency High
Voltage Power
Panel (M/C)

Iwaido Line Line 2L

Tomioka Line 2L

Tomioka Line 1L

Tomioka Line 2L,
Suspended(Suspended after theearthquake but
before the tsunami)

Emergency High
Voltage Power
Panel (M/C)

Emergency High
Voltage Power
Panel (M/C)

Emergency High
Voltage Power
Panel (M/C)

Fukushima Daini Nuclear Power Station
Out of service for check and maintenance
Trip (Suspended)
Circuit Breaker
Dis-connector
Transformer
Main Power Generator

Fig 3.4.1-1 Fukushima Daini Outline Diagram of External Power Supply

18

3.4.2 Damage by the tsunami(1)

Entry of flood water into Main building (Ref: Fig 3.4.2-1, 3.4.2-2)

Inundation surrounding the main buildings of Fukushima Daini (reactor building andturbine building; Ground Level OP +12 m) was not significantly deep, with the
exception of intensive run up on the south side of Unit 1.
Intensive tsunami run up entered the Unit 1 building through the openings at groundlevel located on the south side of the reactor building (air intake louver for the
emergency D/G, equipment hatch on the ground level) which flooded the reactor
building (annex building) and caused the loss of function of all three units ofemergency D/G, emergency power supply (for the C system and high pressure corespray system).
The depth of run up around Unit 2 through Unit 4 was not significant, and thus flooding
into the reactor buildings or turbine buildings through the openings at ground level was
not detected. However, flooding was confirmed in the basement of the reactor buildingof Unit 3 (Annex) and the basements of turbine buildings Unit 1 through Unit 3. It isthought that tsunami inundation entered the buildings through the cables and pipes
leading to the underground trenches and ducts.

Seawater Heat
Exchanger Building

Unit 4

Turbine Building

Unit 3

Unit 2

Unit 1

Reactor Building

Openings on the ground where the flood entered
the main building
Openings leading to the underground trench
duct where the flood entered the main building

Fig 3.4.2-1 Openings of flood entrance into the main building
Unit 2-4, No significant water entry
through the louver/hatch to the reactor
building annex

Reactor
Building
Annex

Main Reactor
Building
Reactor
Building
Flood Height: Annex
O.P. + about 7 m
Ground Level
O.P. + 12 m

Reactor
Building
Annex

Equipment Hatch

Power Panel

Power Panel

Seawall

Main Reactor
Building

Reactor
D/G Air
Intake Building Annex
LouverEquipment Hatch
Seawater Heat
Exchanger Building
Ground Level Building
Entrance
O.P. + 4m

Unit 1, Water entry throughlouver/hatch to the reactor
building annex

Drainage Pump

Fig 3.4.2-2 Flow path of flood to the main buildings of Fukushima Daini

19

Table 3.4.2-1 Location of D/G and damages thereto
Unit 1

Unit 2*1

Height of tsunami
Ground Level
Flood depth aroundmain buildings[Inundation Height]

Building
where D/G
is installed[Floor]

Unit 3

Unit 4

About +9 m
O.P.+12 m
Less than 2.5 m (nearly zero except around Unit 1)[O.P .about+12 m~+14.5 m] *2

AReactor Bldg.
Annex
[B2F]

Reactor Bldg.
Annex
[B2F]

Reactor Bldg.
Annex
[B2F]

Reactor Bldg.
Annex
[B2F]

B

Reactor Bldg.
Annex
[B2F]

Reactor Bldg.
Annex
[B2F]

Reactor Bldg.
Annex
[B2F]

Reactor Bldg.
Annex
[B2F]

H

Reactor Bldg.
Annex
[B2F]

Reactor Bldg.
Annex
[B2F]

Reactor Bldg.
Annex
[B2F]

Reactor Bldg.
Annex
[B2F]

□:D/G unit flooded□:D/G unit not flooded*1*2

Estimate at tide station. Actual measurement unknown because of
instrument damage.
Locally about OP+15 – 16 m [flood depth about 3 – 4 m] in the area
between the south side of the Unit 1 main building and the importantquake proof building.

(2) Damage situation
Among the equipment for reactor cooling that was also damaged by the tsunami, thedamage situation of the facilities that clearly show characteristics of equipment
damage caused by the recent tsunami is explained as below.(Please refer to Table
3.4.2-2.)① Emergency equipment cooling pump
Units 1 through 4 use seawater to remove decay heat from the reactor. The emergency
D/G unit also uses seawater to cool its engine. Therefore, the pumps for the emergency
equipment cooling water system (the seawater intake pump and the fresh water coolingpump sourced from seawater) are installed in the seaside area. These pumps are installedin the seawater heat exchanger building. The purpose of the overall layout in which
seawater is not sent directly to the reactor building but to the intermediate seawater heatexchanger building, which is not a radiation control area, where a freshwater loop is
installed with a heat exchanger and cooling pump for auxiliary equipment constituting an
independent set of equipment cooling facilities, is to prevent seawater from mixing withreactor water and to improve maintenance works. The pumps for the emergency
equipment cooling water system are specified for outdoor use, but they were installedindoors in the heat exchanger building as part of the independent set of equipment coolingfacilities. The ground level of the seaside area where the pumps for the emergency
equipment cooling water system are installed had OP +4 m elevation, and its precautionary
measures ensured safety against a tsunami height of 5.1 - 5.2 m, based on the tsunami
height evaluation results in 2002 provided by the Japan Society of Civil Engineers“Tsunami Evaluation Technology”. However, this tsunami greatly exceeded expectations,and the motors of the pumps were submerged under the water and the system lost
function. The pumps for the emergency equipment cooling water system at Fukushima
Daini were housed in the seawater heat exchanger buildings. The area surrounding thebuildings was inundated to a depth of 3 m by the tsunami, and while there was no damage
to the building structures, all the seawater heat exchanger buildings were flooded byseawater through the damaged doors and other openings on ground level. As a result, the20

power panels and the motor of the pumps were submerged underwater and the total ofeight emergency equipment cooling water systems lost function except for one system of
Unit 3. In addition, the cooling system of the three D/G units, A, B and H installed for eachreactor Unit also lost all function except for three systems: B and H of Unit 3 and H of Unit
4.
② Power panel
The scale of the tsunami at Fukushima Daini was different from that at Fukushima Daiichi,
and inundation of the main building was also different. Accordingly, the situations of power
panel damage also differ as a result.
The Reactor building of Unit 1 (Annex), which was flooded by the tsunami, saw inundationon the emergency power panels of the C and H systems, but the D system power panel
was not flooded and all the power panels of other reactor Units were free of damage. Dueto this situation, it was possible to distribute electric power received from outside sources
to various pieces of equipment through these emergency circuits, making it possible to use
the necessary facilities to cope with the emergency situation (distribution through Normal A
and B2, Emergency C and D2, and high pressure core spray system H). On the other
hand, the power panels in the seawater heat exchanger buildings located in the seaside
area were all submerged in the tsunami because of flooding in the buildings, and sevenpower panels lost function, with the exception of one low voltage power panel (P/C)
situated in the seawater heat exchanger building of Unit 3.
Therefore, the residual heat removal seawater system lost function except for one system
of Unit 3 out of the total of eight.

Table 3.4.2-2 Damage situation of the cooling pumps for emergency equipment andemergency P/C located in the seawater heat exchanger buildings after the tsunami
Locationof
Installati
on

Seawater Pump (RHRC, RHRS and LLCW)
Unit 1
Unit 2
North side
South side
North side
South side

○ Usable △ Out of service due to flooding of Power Panel× Out of service due to flooding of Power Panel and Motor

Unit 3
North side
South side

Unit 4
North side
South side

2nd
Floor
Ground Floor
Location GrouofndInstallati
Floor
on

Emergency P/C
Unit 1
North side
South side

○ Usable× Out of service due to flooding

Unit 2
North side
South side

21

Unit 3
North side
South side

Unit 4
North side
South side

③ Emergency Diesel Generator
In the Fukushima Daini power station, each reactor Unit has three (A, B, H) emergency
diesel generators (hereinafter referred to as "emergency D/G"). Unit 1 lost all three
emergency D/Gs because the tsunami had entered the reactor building (Annex) through the
opening at the ground level. Some of the emergency D/Gs which were able to avoid theflooding still lost function because of the loss of diesel engine cooling due to the flooding of
the power panel and the pump motor for the cooling system. The cooling system of theemergency D/G was lost for most of the systems except for three: B and H of Unit 3 and H
of Unit 4. As a result, nine D/Gs lost function: A, B and H of Unit 1, A, B and H of Unit 2, A of
Unit 3 as well as A and B of Unit 4.
However, Fukushima Daini had a continuous supply of electric power from the externalsources and there was no need to activate such surviving emergency D/G after all.
④ Situation of other outdoor damage
In the Fukushima Daini power station area, no major equipment and/or structure wasobserved being washed up by the tsunami to the main building area (elevation OP +12 m).
However, five cases of openings/holes caused by the tsunami washing away or damaging
the lid of the hatch duct in the main building area have been reported.
Source;Tokyo Electric Power Company
The impact of Tohoku-Chihou Taiheiyo-Oki Earthquake to Nuclear Reactor Facilities at
Fukushima Daini Nuclear Power Station (May 9, 2012)
Fukushima Nuclear Accident Analysis Report (June 20, 2012)
Investigation Committee on the Accident at the Fukushima Nuclear Power Stations of Tokyo
Electric Power Company
Final Report (July 23, 2012)22

4. Response to the accident at Fukushima Daini
The status of the accident at Fukushima Daini has already been reported in detail in thereports of TEPCO and the Investigation Committee of the Government. Therefore, this reportputs the emphasis on describing the situation, including points of suggestion in considering
the lessons learned, and giving a brief overview of the other points.
Fig 4-1 shows the operational status of the responses of Units 1 through 4, and Figs 4-2 to 4-5
show the operational status of each Unit in conjunction with the changes in the main
parameters of each Unit.

23

12:00March 1116:00 20:00

0:00

4:00

March 12
8:00
12:00

16:00

20:00

0:00

4:00

March 13
8:00
12:00

16:00

▽15:33 CWP(C) Manual stop▲▽15:34 Emergency D/G A, B and H automatic start followed by immediate trip
▲15:36 MSIV manual full-close
Water injection by RCIC (15:36 – 4:58)

Unit 1▽15:57 CWP(A,B) Automatic stop
▲Rapid depressurization (3:50 – 4:56)]▲15:50～asappropriate▲0:00 MUWC alternative water injection start
Reactor
S/C cooling by FCS cooling water (MUWC)（6:20～7:20）
depressurization▲D/W spray (7:10 – as appropriate)▲S/C spray (7:37 – as appropriate)

20:00

0:00

4:00

March 14
8:00
12:00

20:00

0:00

March 15
8:00
12:00

4:00

16:00

20:00

0:00

4:00

March 16
8:00
12:00

16:00

20:00

0:00

▲20:17 RHRS(B) Manual start▲21:03 RHRC(D) Manual start▲1:24 RHR(B) Start  Call-off pursuant to Article 10 of the Act on Special Measures Concerning Special Law for Nuclear Emergency▲3:39 S/C spray by RHR (B) start▲10:05 Reactor water injection by means of RHR (B) LPCI mode
▲1:44 Emergency component cooling system (B) manual start▲16:30 SFP water injection by FPMUW start▲20:26 FPC (B) circulation operation start▽9:40 MUWC alternative water injection Stopped

Configuration of pressure proof vent-line (10:21 – 18:30)▲17:53 D/W cooling system manual start

16:00▲0:42RHR(B) SFP cooling start▲17:00 Reactor cold shutdown▲10:30 SFP water temperatureapproximately 38°C (before
earthquake)

Report pursuant to Article 10 of the Act on Special Measures Concerning Special Law for Nuclear Emergency (loss of reactor heat removal function) (18:33 on March 11 – 1:24 on March 14)

Report pursuant to Article 15 of the Act on Special Measures Concerning Special Law for Nuclear Emergency (loss of pressure suppression function) (5:22 on March 12 – 10:15 on March 14)▲▽15:34 Emergency D/G H automatic start followed by immediate trip
▲15:34 MSIV manual full-close▲15:35 RHR(B) Manual start▽15:35 CWP(C) Manual stop, (A and B) automatic stop
▽15:38 RHR(B) Stop▲▽15:41 Emergency D/G A and B automatic start followed by immediate trip

▲3:20 Emergency component cooling system (B) manual start▲3:51 RHRS(B) Manual start▲5:52 RHRC(B) Manual start▲7:13 RHR(B) Start (S/C cooling mode)  Call-off pursuant to Article 10 of the Act on Special Measures Concerning Nuclear Emergency▲7:50 RHR(B)S/C Spray start▲10:48 Reactor water injection by means of RHR (B) LPCI mode

Water injection by RCIC (15:41 – 4:53)
Unit 2

Configuration of pressure proof vent-line (10:33 – 10:58)▲20:02 D/W cooling systemmanual start▲4:50 MUWC alternative water injection start▲D/W spray (7:11 – as appropriate)▲S/C spray (7:35 – as appropriate)▲18:00 Reactor cold shutdown▲1:28 RHR(B) SFP cooling start▲
10:30 SFP water temperatureapproximately 32.5°C (before
earthquake)▽10:12 MUWC alternative water injection stopped

S/C cooling by FCS cooling water (MUWP) (6:20 – 7:52)
Report pursuant to Article 10 of the Act on Special Measures Concerning special Law Nuclear Emergency Preparedness (loss of reactor heat removal function) (18:33 on March 11 – 7:13 on March 14)
Report pursuant to Article 15 of the Act on Special Measures Concerning Special Law for Nuclear Emergency (loss of pressure suppression function) (5:32 on March 12 – 15:52 on March 14)

Unit 3▽15:34 CWP(C) Manual stop▲▽15:35 Emergency D/G A, B and H automatic start followed by immediate trip of A
▲9:37 RHR(B) Manual start (commencement of SHC)
▲15:36 RHR(B) S/C cooling start▲19:46 RHR(B) S/C cooling  Switch to LPCI mode
▲20:07 RHR(B) LPCI mode  Switch to S/C cooling▲0:06 RHR(B) Commencement of configuration of SHC mode system▽1:23 RHR(B) Manual stop, prepare for SHC mode being on▲2:39 RHR(B) Manual start (S/C cooling start)▲2:41 RHR(B)S/C Spray start▽7:59 RHR(B) Manual stop
▲15:37 MSIV manual full-close▽15:38 CWP(B) Manual stop
Water injection by RCIC (16:06 – 23:58)

Configuration of pressure proof vent-line (12:08 – 12:13)▲17:42 FPC Hx cooling water switch-over (RCW  RHRC)▲12:15 Reactor cold shutdown▽16:48 CWP(A) Manual stop
▲20:12 D/W cooling system manual start▲
22:30 SFP water temperature approximately
32.5°C (before earthquake)▲22:53 MUWC alternative water injection start (unknown when stopped)▽15:33 CWP(C) Manual stop▲▽15:34 Emergency D/G A, B and H automatic start followed by immediate trip of A and B▲11:17 HPCS pump start (S/C agitation operation)▽15:34 CWP(A,B) Automatic stop
▲15:36 MSIV manual full-close▲12:32 Reactor water injection switch-over (MUWC  HPCS)▲15:36 RHR(A,B) Manual start▽13:48 Water injection by HPCS stop
▽15:38 RHR(A) Manual stop
▽15:41 RHR(B) Automatic stop
Unit 4▲11:00 Emergency component cooling system (B) manual start▲13:07 RHRS(D) Manual start▲14:56 RHRC(B) Manual start▲15:42 Start (S/C cooling mode)  Call-off pursuant to Article 10 of the Act on Special Measures Concerning Special Law for Nuclear Emergency▲16:02 RHR(B)S/C Spray start▲18:58 Reactor water injection by means of RHR (B) LPCI mode start

Water injection by RCIC (15:54 – 0:16)▲19:14 D/W cooling system manual start▽17:25 MUWC alternative water injection stopped▲0:16 MUWC alternative water
injection start ▲7:35 Alternative containment vessel spray start▲7:15 Reactor cold shutdown▲16:35 FPC Hx cooling water switch-over (RCW → RHRC)

S/C cooling by FCS cooling water (MUWP)（7:23 – 22:14）
Configuration of pressure proof vent-line (11:44 – 11:52)
Report pursuant to Article 10 of the Act on Special Measures Concerning Special Law for Nuclear Emergency (loss of reactor heat removal function) (18:33 on March 11 – 15:42 on March 14)
Report pursuant to Article 15 of the Act on Special Measures Concerning Special Law for Nuclear Emergencys (loss of pressure suppression function) (6:07 on March 12 – 7:15 on March 15)▲Around 22:00 Commence site observation (around Hx / B)

▲Around 6:00 Equipment and materials arrived▲Around 23:30 Completion of temporary cable-laying▲Before dawn: Cable-laying, Unit 1 being of priority (Unit 2  Unit 1)

Chart 4-1: Situation of action in response to the Unit 1 – Unit 4 accident
24▲
20:59 RHR(B) SFP cooling start(7:30 on March 18: SFP water temperature approximately 35°C
(before earthquake))12:00
Unit 1March 1116:00 20:00

0:00

4:00

March 12
8:00
12:00

16:00

20:00

0:00

4:00

March 13
8:00
12:00

16:00

20:00

0:00

March 14
8:00
12:00

4:00

▽15:33 CWP(C) Manual stop▲▽15:34 Emergency D/G A, B and H automatic start followed by immediate trip
▲15:36 MSIV manual full-close
Water injection by RCIC (15:36 – 4:58)

20:00

0:00

March 15
8:00
12:00

4:00

16:00

20:00

0:00

4:00

March 16
8:00
12:00

16:00

20:00

0:00

▲17:00 Reactor cold shutdown▽15:57 CWP(A,B) Automatic stop
▲15:50 – as appropriate ▲Rapid depressurization (3:50 – 4:56)
Reactordepressurization

16:00▲0:00 MUWC alternative water injection start
S/C cooling by FCS cooling water (MUWC) (6:20 – 7:20)▲D/W spray (7:10 – as appropriate)▲S/C spray (7:37 – as appropriate)▽9:40 MUWC alternative water injection stopped
Configuration of pressure proof vent-line (10:21 – 18:30)▲20:17 RHRS(B) Manual start▲17:53 D/W cooling systemmanual start▲21:03 RHRC(D) Manual start▲1:24 RHR(B) Start  Call-off pursuant to Article 10 of the Act on Special Measures Concerning Special Law for Nuclear Emergency▲3:39 S/C spray by RHR (B) start▲10:05 Reactor water injection by means of LPCI mode
▲1:44 Emergency component cooling system (B) manual start▲16:30 SFP water injection by FPMUW start▲20:26 FPC（B) Circulation operation start▲0:42 RHR(B) SFP cooling start▲10:30 SFP water temperatureapproximately 38°C (before
earthquake)

Report pursuant to Article 10 of the Act on Special Measures Concerning Special Law for Nuclear Emergency (loss of reactor heat removal function) (18:33 on March 11 – 1:24 on March 14)

Report pursuant to Article 15 of the Act on Special Measures Concerning Special Law for Nuclear Emergency (loss of pressure suppression function) (5:22 on March 12 – 10:15 on March 14)

[MPa]

[mm]
6000

8.0
7.0

5000

6.0
4000

Reactor water level [mm] (fuel area conversion)

3000

Reactor pressure [MPa]

5.0
4.0

Measurement missing
due to paper jam

2000

3.0
2.0

1000
0
12:00

1.0
16:00

20:00

0:00

4:00

8:00

12:00

16:00

20:00

0:00

4:00

8:00

12:00

16:00

20:00

0:00

4:00

8:00

12:00

16:00

20:00

0:00

4:00

8:00

12:00

16:00

20:00

0:00

4:00

8:00

12:00

16:00

20:00

[kPa]

0.0
0:00

[°C]

450

160

400

140

350

120

300
250

D/W pressure [kPa abs]

200

S/C pressure [kPa abs]

150

S/C water temperature [°C]

100
80
60

100

40

50

20

0
12:00

16:00

20:00

0:00

4:00

8:00

12:00

16:00

20:00

0:00

4:00

8:00

12:00

16:00

20:00

0:00

4:00

8:00

12:00

16:00

20:00

0:00

4:00

8:00

Chart 4-2: Situation of action in response to accident and plant parameter of Unit 1
25

12:00

16:00

20:00

0:00

4:00

8:00

12:00

16:00

20:00

0
0:00

12:00
Unit 2

March 1116:00 20:00

0:00

4:00

March 12
8:00
12:00

16:00

20:00

0:00

4:00

March 13
8:00
12:00

16:00

20:00

0:00

March 14
8:00
12:00

4:00

16:00

▲▽15:34 Emergency D/G H automatic start followed by immediate trip
▲15:34 MSIV manual full-close▲15:35 RHR(B) Manual start▽15:35 CWP(C) Manual stop, (A and B) Automatic stop
▽15:38 RHR(B) Stop▲▽15:41 Emergency D/G A,B Automatic start followed by immediate trip
Water injection by RCIC (15:41 – 4:53)

20:00

0:00

4:00

March 15
8:00
12:00

16:00

20:00

0:00

4:00

March 16
8:00
12:00

16:00

20:00

0:00

▲18:00 Reactor cold shutdown▲15:41 – as appropriate Reactor depressurization as▲20:02 D/W cooling system manual start▲4:50 MUWC alternative water injection start▲D/W spray (7:11 – as appropriate)▲S/C spray (7:35 – as appropriate)▽10:12 MUWC alternative water injection stopped▲3:20 Emergency component cooling system (B) manual start

S/C cooling by FCS cooling water (MUWP) (6:20 – 7:52)
Configuration of pressure proof vent-line (10:21 – 18:30)▲3:51 RHRS(B) Manual start▲5:52 RHRC(B) Manual start▲7:13 Start (S/C cooling mode)  Call-off pursuant to Article 10 of the Act on Special Measures Concerning Special Law for Nuclear Emergency▲7:50 RHR(B) S/C spray start▲10:48 RHR(B) Reactor water injection by means of LPCI mode
▲1:28 RHR(B) SFP cooling start

Report pursuant to Article 10 of the Act on Special Measures Concerning Special Law for Nuclear Emergencys (loss of reactor heat removal function) (18:33 on March 11 – 7:13 on March 14)▲
10:30 SFP water temperatureapproximately 32.5°C (before
earthquake)

Report pursuant to Article 15 of the Act on Special Measures Concerning Special Law for Nuclear Emergency (loss of pressure suppression function) (5:32 on March 12 – 15:52 on March 14)

[mm]

[MPa]
8.0

6000

7.0

5000

6.0
4000

Reactor water level [mm] (fuel area conversion)

3000

Reactor pressure [MPa]

5.0
4.0
3.0

2000

2.0
1000
0
12:00

1.0
16:00

20:00

0:00

4:00

8:00

12:00

16:00

20:00

0:00

4:00

8:00

12:00

16:00

20:00

0:00

4:00

8:00

12:00

16:00

20:00

0:00

4:00

8:00

12:00

16:00

20:00

0:00

4:00

8:00

12:00

16:00

20:00

[°C]

[kPa]
450
400
350

160

●:D/W圧力 [kPa abs]●:S/C圧力 [kPa abs]

140
120

300

100

250
200
150
100

D/W pressure [kPa abs]

80

S/C pressure [kPa abs]

60

S/C water temperature [°C]

40
20

50
0
12:00

0.0
0:00

16:00

20:00

0:00

4:00

8:00

12:00

16:00

20:00

0:00

4:00

8:00

12:00

16:00

20:00

0:00

4:00

8:00

12:00

16:00

20:00

0:00

4:00

8:00

Chart 4-3: Situation of action in response to accident and plant parameter of Unit 2
26

12:00

16:00

20:00

0:00

4:00

8:00

12:00

16:00

20:00

0
0:00

12:00
Unit 3

March 1116:00 20:00

0:00

4:00

March 12
8:00
12:00

16:00

20:00

0:00

March 13
8:00
12:00

4:00

16:00

20:00

0:00

4:00

March 14
8:00
12:00

16:00

20:00

0:00

4:00

March 15
8:00
12:00

16:00

▲15:37 MSIV manual full-close▲12:15 Reactor cold shutdown▽15:38 CWP(B) Manual stop
▽15:34 CWP(C) Manual stop▲▽15:35 Emergency D/G A, B and H automatic start followed by immediate trip of A

20:00

0:00

4:00

March 16
8:00
12:00

16:00

20:00

0:00

▲17:42 FPC Hx cooling water switch-over (RCW  RHRC)▲
22:30 SFP water temperature approximately
32.5°C (before earthquake)▽15:33 CWP(C) Manual stop▲▽15:34 Emergency D/G A, B and H automatic start followed by immediate trip of A and B
Water injection by RCIC (16:06 – 23:58)▽16:48 CWP(A) Manual stop
▲22:53 MUWC alternative water injection start (unknown when stopped)
Configuration of pressure proof vent-line (12:08 – 12:13)▲11:00 Emergency component cooling system (B) manual start▲9:37 RHR(B) Manual start (SHC start)▲15:36 RHR(B) S/C cooling start▲19:46 RHR(B) S/C cooling  switch-over to LPCI mode
▲20:07 RHR(B) LPCI mode  switch-over to S/C cooling▲0:06 RHR(B) Configuration of SHC mode system start▽1:23 RHR(B) Manual stop (prepare for SHC mode being on)▲2:39 RHR(B) Manual start (S/C cooling start)▲2:41 RHR(B) S/C spray start▽7:59 RHR(B) Manual stop
▲20:12 D/W cooling system manual start

[mm]

[MPa]

6000

8.0
7.0

5000

6.0
4000

5.0

Reactor water level [mm] (fuel area conversion)

Measurement missing
due to paper jam

3000
Reactor pressure [MPa]

2000

4.0
3.0
2.0

1000
0
12:00

1.0
16:00

20:00

0:00

4:00

8:00

12:00

16:00

20:00

0:00

4:00

8:00

12:00

16:00

20:00

0:00

4:00

8:00

12:00

16:00

20:00

0:00

4:00

8:00

12:00

16:00

20:00

0:00

4:00

8:00

12:00

16:00

20:00

[kPa]

0.0
0:00

[°C]
160

450
D/W pressure [kPa abs]
S/C pressure [kPa abs]
S/C water temperature [°C]

400
350

140
120

300

100

250

80

200

60

150
100

40

50

20

0
12:00

16:00

20:00

0:00

4:00

8:00

12:00

16:00

20:00

0:00

4:00

8:00

12:00

16:00

20:00

0:00

4:00

8:00

12:00

16:00

20:00

0:00

4:00

8:00

Chart 4-4: Situation of action in response to accident and plant parameter of Unit 3
27

12:00

16:00

20:00

0:00

4:00

8:00

12:00

16:00

20:00

0
0:00

12:00
Unit 4

March 1116:00 20:00

0:00

4:00

March 12
8:00
12:00

16:00

20:00

0:00

March 13
8:00
12:00

4:00

16:00

20:00

0:00

4:00

March 14
8:00
12:00

16:00

20:00

0:00

4:00

▽15:33 CWP(C) Manual stop▲▽15:34 Emergency D/G A, B and H automatic start followed by immediate trip of A
▲11:17 HPCS pump start (S/C agitation operation)▽15:34d B CWP(A,B) Automatic stop
▲15:36 MSIV manual full-close▲12:32 Reactor water injection switch-over (MUWC  HPCS)▲15:36 RHR(A,B) Manual start▽13:48 Water injection by HPCS stopped▽15:38 RHR(A) Manual stop
▽15:41 RHR(B) Automatic stop

March 15
8:00
12:00

16:00

20:00

0:00

4:00

March 15
8:00
12:00

16:00

20:00

0:00

▲7:15 Reactor cold shutdown

Water injection by RCIC (15:54 – 0:16)▲19:14 D/W cooling system manual start▽17:25 MUWC alternative water injection stopped▲0:16 MUWC alternative water
injection start ▲7:35 Alternative containment vessel spray start
S/C cooling by FCS cooling water start (7:23 – 22:14)▲11:00 Emergency component cooling system (B) manual start▲13:07 RHRS(D) Manual start▲14:56 RHRC(B) Manual start▲15:42 RHR(B) Start (S/C cooling mode)  Call-off pursuant to Article 10 of the Act on Special Measures Concerning Special Law for Nuclear Emergency▲16:02 RHR(B) S/C spray start▲18:58 RHR(B) Reactor water injection by means of LPCI mode start

Configuration of pressure proof vent-line (11:44 – 11:52)▲16:35 FPC Hx cooling water switch-over (RCW  RHRC)▲
20:59 RHR(B) SFP cooling start(SFP water temperature approximately 35°C
(before earthquake))

Report pursuant to Article 10 of the Act on Special Measures Concerning Special Law for Nuclear Emergency (loss of reactor heat removal function) (18:33 on March 11 – 15:42 on March 14)
Report pursuant to Article 15 of the Act on Special Measures Concerning Special Law for Nuclear Emergency (loss of pressure suppression function) (6:07 on March 12 – 7:15 on March 15)

[MPa]

[mm]

6000

8.0
7.0

5000

6.0
4000

5.0

Reactor water level [mm] (fuel area conversion)

3000

4.0
Reactor pressure [MPa]

3.0

2000

2.0
1000
0
12:00

1.0
16:00

20:00

0:00

4:00

8:00

12:00

16:00

20:00

0:00

4:00

8:00

12:00

16:00

20:00

0:00

4:00

8:00

12:00

16:00

20:00

0:00

4:00

8:00

12:00

16:00

20:00

0:00

4:00

8:00

12:00

16:00

20:00

0.0
0:00

[kPa]

[°C]

450

160

400

140

350

120

300

100

250

80

200

D/W pressure [kPa abs]
S/C pressure [kPa abs]
S/C water temperature [°C]

150
100

60
40
20

50
0
12:00

16:00

20:00

0:00

4:00

8:00

12:00

16:00

20:00

0:00

4:00

8:00

12:00

16:00

20:00

0:00

4:00

8:00

12:00

16:00

20:00

0:00

4:00

8:00

Chart 4-5: Situation of action in response to accident and plant parameter of Unit 4
28

12:00

16:00

20:00

0:00

4:00

8:00

12:00

16:00

20:00

0
0:00

4.1 Response status from the time of the earthquake and tsunami until restorationand cold shutdown
Just before the earthquake, all Units 1 through 4 were in operation at the rated power. All
control rods were fully inserted by the automatic scram signal triggered by the earthquake,and all reactors shut down automatically. In this way, the water level in the reactor was
lowered to "(L-3) low reactor water level," but the normal level was recovered without
reaching the level which would automatically activate the emergency core cooling system
by supplying water from the reactor feedwater system. Further, as designed, the "(L-3)
reactor water level low" automatically activated the containment vessel isolation systemand the emergency gas treatment system, and isolation of the containment vessel andnegative pressure of the reactor building were achieved.
After the entry of the tsunami, the main condenser could not be used as a heat sink, so themain steam isolation valve was fully closed manually (core isolation) and reactor pressure
was controlled by the main steam safety relief valve. In this operation, in accordance withthe core isolation operating procedures (when the main steam isolation valve is closed), thereactor core isolation cooling system (hereinafter referred to as "RCIC") was manually
started up in order to control the water level of the reactor by repeating automatic shutdown
and manual start up based on the water level.
The entry of the tsunami caused part of the emergency core cooling system to become
unusable due to the flooding of the pump motor and power source in the seawater system.
Water was injected to the core by RCIC and the main steam safety relief valve was opened
to depressurize the reactor core in order to maintain the alternate water injection(application of Accident Management (AM) procedure) via the condensate water makeup
system (hereinafter referred to as "MUWC"). Before switching over to MUWC, it was
confirmed that water injection via MUWC to the reactor core would be possible with RCICin operation. The water temperature of the S/C rose. Therefore, water was injected to the
S/C using the drain line in the water cooler of the combustible gas control system to cool
down the containment vessel, together with dry well spray and S/C spray. This dry wellspray was executed at the discretion of the Director at the power plant.
The equipment at the south area of the heat exchanger building of Unit 3 was not flooded,
and so the emergency D/G and the residual heat removal system remained operative.
Therefore, Unit 3 was able to achieve cold shutdown using the cooling system that is usedin normal reactor shutdown cooling mode.
An external power supply was available through Tomioka 1L and a number of operations,and monitoring of major parameters were possible at the central control room with little
damage on transformers and power panel, making the emergency responses quick andresulting in early convergence. Expeditious recovery was tried on the damaged line before
it was lost; Iwaido 2L recovered at 1:38 pm on the 12th, and Iwaido 1L recovered at 5:15
am on the 13th. It was fortunate that the plant was able to use Tomioka IL continuously fromthe very beginning without power outage. This situation made it possible to respond to theaccident appropriately and prevented the expansion of the accident.
The development of AM measures such as the use of MUWC contributed significantly tothe convergence of the accident at Fukushima Daini. Also, as another AM measure which
would have been quickly available if the accident situation had rapidly deteriorated, acontainment vent facility was prepared and available, although it was ultimately not usedbecause of the swift convergence of the accident. When a report was sent to the national
and local governments in accordance with Article 10 of the Nuclear Disaster Special
Measures Law (hereinafter referred to as "Nuclear Emergency Law"), TEPCO explainedthat they were preparing to implement a vent from the containment vessel.
In parallel with the response operations described above, the plant’s emergency
headquarters (hereinafter referred to as "Headquarters") made a thorough check of the29damage at the site, ensured the supply of necessary equipment for restoration (motors,
high-voltage power supply cars, transformers, cables, etc.) in consultation with the
emergency headquarters at the head office and developed a recovery plan for the residual
heat removal system, taking into account the priority.
Upon the arrival of the recovery equipment, power cables were installed and pump motors
were replaced simultaneously, and the pumps for the residual heat removal system were
put in motion within two or three days after the entry of the tsunami.
As a result of the residual heat removal system starting up, all the Units had access tocooling by S/C and the usual reactor cooling water, which ensured the cold shutdown of all
reactors.
About two days after cold shutdown, Units 1, 2, and 4 experienced a tendency of risinghydrogen concentration in the containment vessel. However, the operation of the
flammable gas control system successfully suppressed the hydrogen concentration below
the level at which a mix of hydrogen and oxygen concentration becomes flammable, andthere was no danger of a hydrogen explosion. It is theorized that the hydrogen was
generated by chemical reactions of zinc and aluminum in the containment vessel.
4.2 Emergency response situation
4.2.1 Immediately after the earthquake
As a result of the big earthquake and the scram of the plant, an emergency situation was
declared and key members of the emergency disaster management system assembled
immediately at the Headquarters in the important seismically isolated building. The
manual calls for seven teams and 250 personnel in the emergency disastercountermeasures organization. (See Fig 4.2.1-1.) Because it was a weekday afternoon,
there were approximately 400 engineering staff on duty in the plant office and all of themwere incorporated into the emergency disaster management system. All of these
employees stayed in the Headquarters or in the office and engaged in accident response
in rotation in accordance with their physical capabilities until the morning of March 15,
when the reactors were brought to cold shutdown and the situation calmed down tosome extent.
As from around 8 pm on the 11th when the tsunami situation subsided, the site patrol had
started to check the status of the equipment. Various works requiring much manpower
continued thereafter: draining water from the building, laying cables for restoration,
deploying vehicles to ensure a landing site for helicopters bringing relief supplies, andtransportation of goods, etc.
The operators in the central control room were engaged in plant control and monitoring
accident responses in a normal rotational shift. The central control rooms of Fukushima
Daini, as a twin plant system, are each shared by two Units: Units 1 and 2, and Units 3
and 4, respectively. Each control room has one shift supervisor, one deputy s/v, twoforemen, one deputy foreman, two main system operators, and three sub system
operators, totaling 10 persons per shift.
In addition, a part of about 1,900 employees of cooperating companies who were
present in the plant at the time were also involved in the recovery efforts.
With regard to TEPCO employees, a contact network for mobilization at night or on
holidays had been established, and a special contact person was assigned to mobilize
the employees of cooperative enterprises. Therefore, if this accident had happened atnight or on a holiday, these network channels would have been used for the mobilizationof manpower. However, when mobilizing at night or on a holiday, it takes substantiallylonger for people to convene than with an immediate input of manpower like there wasthis time, meaning that the initial response to the accident could not have been as quick30

or smooth as it was this time.
The Headquarters dispatched an experienced operator each as a contact courier to bothof the central control rooms for Units 1/2 and Units 3/4 to provide a variety of information
to the Headquarters and also to transmit instructions from the Headquarters to thecontrol rooms. Dispatching such operators is not a procedure prescribed in the manual,
but it was put into practice between the teams to define their roles and responsibilities,
especially in the case of troubleshooting.
Contact with the local government was maintained using the direct lease line and thesatellite phones of the power plant when ordinary telephone and FAX lines wereinterrupted because of the disruptions of communication lines.
As long as the power supply to the Headquarters was online, contact with the head office
was possible via PHS and video conference for effective information sharing. This videoconference system was also connected with Kashiwazaki-Kariwa Nuclear Power Station(hereinafter referred to as "Kashiwazaki-Kariwa"), which was able to join the videoconference at the same time.
Despite the severity of the earthquake tremors, nobody at the plant office had sufferedinjuries and so initial response was started right away, thanks to the practicalcountermeasures as a reflection of the lessons of the Chuetsu-oki Earthquake, such as
thorough works to prevent cabinets from tipping. The central control room has a grip bar
attached to the control panel, also as a reflection of such lessons, so that the operator
can hold onto the grip during tremors and keep their eyes on the panel and continue
operation, which proved to be effective in this earthquake. Thanks to day-to-day efforts
for preparedness, the main control room did not experience any disruption orinterference from the movement of large objects due to the quake.
Of the documents and drawings needed for restoration works, the materials prescribedin the disaster plan, such as P&ID, were stored in the important seismically isolatedbuilding. Other drawings, such as those of individual hardware like valves and pumps,
were retrieved from the library of the main office building. Since the library was free fromearthquake and tsunami damage, there were no problems in the search for thesereference materials.

31

InformationTeam

1. Send and receive information to and from theheadquarterｓ at the Head Office
2. Information gathering from teams

Communicatio
1. Communication with outside organizationn TeamHeadquarters Overall Management
and Administration
Director Nuclear Safety
Administrator (Plant Manager)

PublicRelationsTeam

1. Public relations with mass media

Technical
Team

1. Grasp and assess accident situation
2. Estimate area affected by accident
3. Study preventive measures against accident expansion

Safety Team

1. Grasp situation of radiation hazards inside and outsidesite
2. Control exposure and contamination
3. Estimate area affected by radiation

Restoration
Team

1. Planning and execution of emergency response plan
2. Planning of accident restoration schedule
3. Fire fighting

Power
Generation
Team

1. Grasp accident situation
2. Assignment of operators to prevent accident expansion
3. Maintenance and safety of equipment in plant

Materials
Team

1. Procurement and transportation of materials
2. Procurement of mobility measures

Welfare Team

1. Procurement of food and clothing
2. Arrangement of lodging

Medical Team 1. Medical activities

1. Publicity to on-site personnel
General
2. Secretariat of emergency headquarters
Administration
3. Call-up and transportation of manpowerTeam
4. All other tasks and chores

Security andGuidanceTeam

1. Safeguarding site
2. Evacuation and guidance of visitors from outside
3. Operation of physical protection facilities

Fig 4.2.1-1 Emergency response organization

32

4.2.2 Immediately after the arrival of the tsunami
By the time the tsunami arrived, seawater had entered into the seawater heat exchanger
building built on the ground at 4 m elevation, and the pumps for the emergency
equipment cooling water system had lost function. Since a tsunami warning was issued
after the earthquake, preparations were in place for the entry of the tsunami. After thearrival of the first wave of the tsunami, one circulating water pump was manually shut
down based on the manual for tsunami backwash precautions. The other two pumps,
however, also shut down automatically due to the impact of the tsunami. (All pumps ofUnit 3 were manually shut down.) The lamp display on the control panel of the central
control room could confirm the shutdown of these seawater pumps.
Starting from around 2003, precautionary measures for tsunamis had been gradually
carried out for the seawater heat exchanger building by installing watertight doors,strengthening the pipe penetration seal, and measures to prevent water entering
manholes. However, these measures assumed only a tsunami height of 5.1 m to 5.2 m inaccordance with the 2002 evaluation results and were not able to prevent the entrance oftsunami seawater in this incident, where it was far higher than the height assumed in the
precautions. Nonetheless, as the equipment was installed in the building, it was not
destroyed or washed away and the loss of function was caused mainly by water damage
due to the tsunami.
The tsunami reached the start-up transformer but it was not submerged to a significant
extent, so it was able to maintain its function.
As soon as the entry of the tsunami calmed down, patrollers were dispatched to inspect
the status of the equipment which had lost function in order to evaluate whether function
could be restored through minor repair and maintenance. The patroller team consisted ofeach group of the restoration team. Patroller clothing and gear, such as helmets andflashlights, was as usual except for a pair of long boots for entering buildings flooded byseawater. The PHS signal was not reliable and the paging system in the area had lost
function because of the tsunami. In order to ensure the delivery of any further tsunami
warnings to patrollers while on patrol, a liaison was placed with a PHS phone to be kept
connected at all times, who would deliver evacuation instructions to patrollers if andwhen warnings were issued.
Patrollers performed visual inspection and rough measurement of the equipment todetermine whether it was functional. Their findings were illustrated in matrix form on awhiteboard in the Headquarters to share the information with everybody and were used
to develop the recovery plan.
Electric power to the seismic isolation building, where the Headquarters was set up, hadbeen supplied by an external power source; however, the onslaught of tsunami water
caused a blackout. The plant had an emergency gas turbine generator but due toflooding, it did not start up either. At around 7 pm on the 11th, the power supply to theimportant seismic isolation building was restored by laying a cable from the external
power source via the main office building. At around 11 pm, SPDS was restarted andmonitoring of the plant situation was resumed. Until SPDS was restarted, suchmonitoring had relied on the information brought back by the experienced operators
dispatched to the central control room. After SPDS resumed, the Headquarters was able
to monitor and confirm various parameters of the displayed plant right away in order todevelop a recovery plan. Security telephones were also available and used as acommunication channel.

33

4.2.3 Responses toward restoration after the arrival of the tsunami
4.2.3.1(1)

Overview of the power plant

Responses and operations at the Headquarters

All works toward the restoration had been done only by the Fukushima Daini staff
stationed at the site from the beginning, except for the support staff dispatched fromthe Power Distribution Department for restoration works on the power supply. The total
number of support staff from the Distribution Department during the work period fromMarch 11 to March 15 was 114 TEPCO employees and 35 cooperating company
employees. These support staff worked on the management of power vehicles andcable laying works. Temporary cables were laid by 11:30 pm on the 13th, in between
the power panel that was not affected by the tsunami, the high voltage power vehicle
and the pump motor, by a combined work force of 200 personnel from TEPCO andcooperating companies (total length of cable in the four Units: approx. 9 km).
All the schedules for work toward restoration were developed by TEPCO employees at
the Fukushima Daini headquarters. The plant manufacturer was not involved in theplanning. In the development of restoration plans, the status of the plant and thesequence of events were carefully evaluated according to a variety of parameters suchas reactor pressure, reactor water level, drywell pressure, S/C pressure, watertemperature at S/C, and water level at S/C. The rate of pressure increase of the S/C
was closely monitored to determine its priority in the recovery works of plants. Thisapproach was based on the common understanding among the staff of the power
plant that the vent from the containment vessel should be avoided as much as
possible so as to minimize the possibility of releasing radioactive materials into theenvironment.
After the recovery of the residual heat removal system, in addition to the cooling of the
S/C, water from the S/C was injected into the reactor from the low-pressure water
injection line using the pump of the residual heat removal system in order to expedite
the cooling of the reactor. At the same time, reactor water was returned to the S/C via
the main steam safety valve, creating a circular flow of water where the water in the
S/C was cooled down by the heat exchanger of the residual heat removal system andreturned again to the reactor via a low-pressure injection line. Emergency Operating
Procedure (EOP) prescribes a procedure where one unit of the residual heat removal
system should be dedicated to the cooling of S/C water, and the other unit should be
dedicated to the cooling of reactor water. In reality, however, there was only one
available residual heat removal system, so this was devised as a practical solution.
Prior to the implementation of this idea, there was thorough discussion by thegeneration team and final approval was given by the power plant manager. The flowrate of the residual heat removal system was 1,300 m3/h in Unit 1, 1,600 m3/h in Unit
2 and 1,400 m3/h in Unit 4 respectively.
The injection of water into the reactor by RCIC caused the water level of the S/C to riseas the steam which drove the RCIC turbine was exhausted into the S/C. So the sourceof water was switched to S/C from CST in order to ensure pressure suppression
capability. After that, since the reactor pressure fell, water injection was switched towater from MUWC, but CST, the source of the MUWC water, was supplied with waterfrom the pure water tank in order to continue the injections into the reactor. In
performing this maneuver, priority was given to CST of Units 1 and 2 because thedecay heat at these units was greater than at Unit 4. Unit 4 at first stirred water in the
S/C, and then switched to water injection by HPCS. The water level in the tanks ofUnits 1 and 2 gradually decreased so the water from the condenser was sent to CST
to secure the water source. After March 16, when the pipeline from the river was
restored, river water was supplied to the filtered water tank. A condensate water pump
was used to transport water from the water condenser but the system to supply the34

water to cool down the pump and motor was inoperable, and use of the condensate
water pump was limited because of the tendency of the pump to heat up.
As for possible instrument failure, continuity of the parameters and cross checking of
the readings between plural instruments were evaluated after the earthquake and the
instruments were duly confirmed to be free from abnormalities.
Given how the tsunami struck, it was easy to assume that the equipment located inseaside areas was damaged, so procurement of cables and power supply vehicles
was arranged without waiting for the results of the patrol. By the time of the patrol on
the night of March 11, the status of the equipment was known and a list of thenecessary equipment had been prepared by the restoration team. Some were directly
requested from the restoration team to Kashiwazaki-Kariwa Plant, and the rest fromthe material team to head office. Kashiwazaki-Kariwa Plant removed motors from theirown system to ship out cooling system motors. These measures were proposed by
Kashiwazaki-Kariwa, which was able to share information via the video conference
system. In regard to requests to cooperating companies in the recovery works, theTEPCO Material Department of the head office had entered into a cooperationagreement with each cooperating company and manufacturer for cooperation andsupport arrangements during "disaster situations" or "emergency situations." On thebasis of this agreement, cooperation was requested for the supply of material and thedispatch of workers.
Equipment and materials were delivered by transport companies and SDF, buttransportation was truly chaotic because of adverse situations such as the national
highway system being cut off, a lack of accurate information on detours or bypasses,
disconnected mobile phones, etc. After the explosion at Fukushima Daiichi, it became
impossible for transport to reach Fukushima Daini directly. Therefore, TEPCO
employees/subcontractor staff went to Hirono Town Hall to pick up the motors or to J
Village for other equipment and materials to transport.
The radiation control equipment was not damaged by the earthquake and tsunami,
and so there was no inconvenience or shortage with regard to the works.
As for the emergency stock of food, the plant already had a stockpile of foods ascountermeasures for the Chuetsu-oki Earthquake and the influenza pandemic,
sufficient for 250 emergency personnel for three days, duty officers for 40 days, and 60
percent of the main office staff for two weeks. In addition, five days of drinking water
were also stockpiled for 250 emergency personnel. Therefore, all personnel at the sitewere able to get by during the first three days, until the 13th when aid materials arrived.
Since the plant had no equipment to make drinking water, the stockpiled drinking waterand food were distributed not only to TEPCO employees but also to the staff andworkers of cooperating companies, and thus, the allocation per capita was decreased
from the second day, making the situation rather grim and tough.
The medical team looked after health and hygiene problems in response to thesituation resulting from a large number of people being forced to work and live in asmall, crowded area. Stress-induced physical problems were also observed later,
necessitating mental health care for the workers.

(2)

On-site restoration works

Since it was possible to receive external power supply via one transmission line,
power was supplied to the equipment in the seawater heat exchanger building, suchas the pump of the residual heat removal seawater system, by laying a cable from the35

power panel of the waste treatment building. Until 11:30 pm on the 13th, all 200
workers, including employees of TEPCO and cooperating companies, finished laying
the temporary cables to directly connect the un-flooded power panel to thehigh-voltage power supply car with the pump motor (total length 9km for 4 plants).
Routing for cable laying was determined in consideration of various factors and theassessment of the overall situation, such as available power panels, distance of cables
to the target equipment, environment in the area to lay the cable, other restrictive
conditions, and the ease of the laying works. The power supply vehicle was used as
the power source for the equipment installed in local areas, such as the EECW pumpsof Unit 1 and Unit 4 located in the seaside area or the river water intake pump. The
power supply vehicle could operate only for few hours at a time because of the volume
of fuel required, so continuous operation was maintained with a refueling teamconducting refueling every three hours. In this situation, ensuring the supply of diesel
oil for the power supply vehicle and gasoline for general vehicles within the site wasdifficult.
Restoration works were suspended at the time of every aftershock and tsunami
warning. Works were also suspended due to evacuation instructions in response to the
Fukushima Daiichi explosion. In addition, starting from the evening of the 14th, when
the air dose rate had increased due to radioactive materials descending from
Fukushima Daiichi, workers were required to wear Tyvek and full-face masks for all
outdoor works. Fig 4.2.3.1-1 shows the rise of the dose rate at monitoring post No. 4 in
the west part of the power plant. (See Fig 2.1 for location details.)
In addition, it was not possible to ensure a sufficient number of workers for some tasks
such as maintenance of office equipment and protective gear, and driving of heavymachinery. TEPCO staff engaged in these tasks.

(3)

Arrangements of personnel and materials/equipments /others

Except for support staff dispatched from the Power Distribution Division for power
recovery, the persons present at Fukushima Daini when the earthquake occurred were
engaged in restoration efforts. From March 11 to 15, all 114 TEPCO employees and 35
cooperating company employees were dispatched as support staff from the PowerDistribution Division. They were engaged in the maintenance of the power supply cars
and support for cable laying.
Transport companies or the Self-Defense Forces carried equipment/materials;
however, transportation was in a state of confusion due to bad conditions such as
blockages of the national roads, insufficient guidance as to detours and disconnectedmobile phones. After the explosion at Fukushima Daiichi, there were difficulties in
directly delivering materials/equipment to Fukushima Daini, and therefore employees
of TEPCO and cooperating companies went to the Hirono Town Office to pick up
motors and to J-Village for other materials/equipment, and then transported them to
Fukushima Daini.

36

1000

100

μSv/h

10

1
2011/3/13 7:40

2011/3/14 3:40

2011/3/14 23:40

2011/3/15 19:40

0.1

0.01
YYYY/MM/DD

Fig 4.2.3.1-1 Monitoring Data at Fukushima Daini (Near MP4)

37

2011/3/16 15:40

2011/3/17 11:40

4.2.3.2

Situation of Fukushima Daini Unit 1.

(1) From the earthquake to immediately after the arrival of the tsunami
At 2:48 pm on March 11, the reactor automatically shut down and at 3:00 pm, it
was confirmed that it had become subcritical.
As a countermeasure against the tsunami (visual confirmation of the arrival of
the first wave at 3:22 pm on March 11), the main steam isolation valve was fully
closed manually at 3:36 pm on March 11and RCIC was activated manually to
inject water into the reactor, and at 3:55 pm on the same day, depressurizationof the reactor by the main steam relief safety valve was begun.
Due to the impact of the tsunami, some of the motors and power panels were
flooded and became unusable. As a result, all of the pumps in the emergency
core cooling system entered a non-bootable state. (At 6:33 pm, the plant
manager determined the situation to be an incident to which Article 10 (loss ofreactor heat removal function) of the Nuclear Emergency Law applies.)(2) Injection of water into reactor and cooling of pressure vessel
Water was injected into the reactor by RCIC but starting at 0:00 am on the 12th,
alternative water injection by MUWC (AM measures) was carried out
concurrently.
Because of the drop in pressure in the RCIC turbine driving steam due to thedecrease in reactor pressure, RCIC was manually isolated at 4:58 am on the
12th and the water level in the reactor was adjusted by alternative water
injection by MUWC thereafter.
The water temperature of the S/C gradually rose due to the operation of RCIC
and the opening of the main steam relief safety valve, and at 5:22 am on the
12th, the water temperature of the S/C reached above 100C. (The plant
manager determined the situation to be an incident to which Article 15 (loss ofpressure control capability) of the Nuclear Emergency Law applies.)
For the cooling of the S/C, starting from 6:20am of the 12th, the injection ofcooling water (MUWC) to the S/C was carried out using the cooling water drainline in the cooler of the flammability gas control system, and dry well spray by
MUWC (starting from 7:10 am on the same day), and S/C spray (starting from
7:37 am on the same day) were conducted from time to time to cool thecontainment vessel.
Because there was an upward tendency in the pressure of the containment
vessel due to the loss of the heat removal function of the reactor, it was
assumed that it would take time to recover the heat removal function of thereactor, and line configuration (completing all necessary actions except one lastaction to open the outlet valve to the S/C) was conducted for the vent of thecontainment vessel between 10:21 am and 6:30 pm on the 12th. However,containment vessel vent was not implemented because the pressure of thecontainment vessel did not reach the level that would require a vent.
(3) Recovery of residual heat removal system and cold shutdown of reactor
At about 10 pm on the 11th, after establishing communication and evacuation
procedures, the restoration team began investigation of the status of tsunami
damage on the seawater heat exchanger building located in the seaside area infull safety gear.
Based on the findings of the investigation of the restoration team, theheadquarters established a restoration plan for the power plant, on a priority
basis, to carry out inspection and repair of pumps in the residual heat removal

38

cooling system located in the seawater heat exchanger building (D), seawater
pumps in residual heat removal system (B), and cooling pumps of emergency
diesel generator (B) (while the motor of the pump in the residual heat removal
cooling system and the cooling pump of the emergency diesel generator were to
be replaced). Headquarters asked the Kashiwazaki-Kariwa Nuclear Power Plant
for the urgent supply of motors.
The equipment and materials for which procurement was requested of theheadquarters of the head office and the Kashiwazaki-Kariwa plant arrived at
Fukushima Daini by 6:00 am on the 13th.
Temporary cables were laid from the power panel of the waste treatmentbuilding through the south side of the reactor building of Unit 1, which was notaffected by the tsunami, to connect directly with the motor. Also, another cable
was laid from the power transformer installed at the large equipment entrance ofthe turbine building of Unit 3. In parallel to the cable laying, the status of themechanical parts of the pump were checked and mounting of the motor was
carried out, and at 8:17 pm on the 13th, the seawater pump of the residual heatremoval system started up.
At 1:24 am on the 14th, the pump of the residual heat removal system (B)started in S/C cooling mode, and the plant manager concluded that this situation
signified the end of the situation of Article 10 of the Special Law for Nuclear
Emergency (loss of reactor heat removal function).
As a result of the cooling of the S/C in the (B) pump in the residual heat removal
system, the S/C temperature declined gradually and dropped below 100C at
10:15 am on the 14th, and the plant manager concluded that the situation had
recovered from the situation of Article 15 (the loss of pressure suppressionfunction) under the Special Law for Nuclear Emergency.
In order to cool down the reactor water expeditiously, in addition to cooling of the
S/C, at 10:05 am on the 14th, injection of water from S/C into the reactor fromthe low-pressure water injection line using the pump of the residual heat removal
system (B) began. At the same time, reactor water was returned to the S/C via
main steam safety relief valve after cooling down the water in S/C using the heatexchanger of the residual heat removal system and returning it again to thereactor via a low-pressure injection line, making for a circular flow of water (S/C pump in the residual heat removal system (B)  heat exchanger in theresidual heat removal system (B)  low-pressure water injection line  reactor
 main steam safety relief valve  S/C), as a temporary measure.
The temperature of the reactor water dropped below 100C at 5:00 pm of thesame day and cold shutdown was achieved.
At 5:12 am on March 16, about two days after cold shutdown, the monitor of thecontainment vessel showed a rising tendency of hydrogen concentration(Hydrogen Approx.5%, Oxygen Approx. 2%). Therefore, the flammable gas
control system was operated and hydrogen and oxygen concentration was
successfully controlled below the flammable level of concentration.
4.2.3.3

Situation of Fukushima Daini Unit 2.

Except for minor differences in the time frame, the operation and actions in Unit 2 were
essentially same as those at Unit 1.
(1) From the earthquake to immediately after the arrival of the tsunami
At 2:48 pm on March 11, the reactor automatically shut down and at 3:00 pm on

39

the same day, it was confirmed that the reactor it had become subcritical.
As a countermeasure against the tsunami (visual confirmation of the arrival of
the first wave at 3:22 pm on March 11), the main steam isolation valve was fully
closed manually at 3:34 pm on March 11 and RCIC was activated manually to
inject water into the reactor, and at 3:41 pm on the same day, depressurizationof the reactor began via the main steam relief safety valve.
Due to the impact of the tsunami, some of the motors and power panels were
flooded and became unusable. As a result, all of the pumps in the emergency
core cooling system entered a non-bootable state. (At 6:33 pm on the same day,the plant manager determined the situation to be an incident to which Article 10(loss of reactor heat removal function) of the Special Law for Nuclear Emergency
applies.)(2) Injection of water into reactor and cooling of pressure vessel
Water was injected into the reactor by RCIC but starting at 4:30 am on the 12th,
alternative water injection by MUWC (AM measures) was carried out
concurrently.
Because of the pressure drop in the RCIC turbine driving steam due to thedecrease in the reactor pressure, RCIC was manually isolated at 4:53 am on the
12th and the water level in the reactor was adjusted by alternative water
injection by MUWC thereafter.
The water temperature of the S/C gradually rose due to the operation of RCIC
and the opening of the main steam relief safety valve, and at 5:32 am on the
12th, the water temperature of the S/C reached above 100C. (The plant
manager determined the situation to be an incident to which Article 15 (loss ofpressure control capability) of the Special Law for Nuclear Emergency applies.)
For the cooling of the S/C, starting from 6:30 am of 12th, injection of coolingwater (MUWC) to the S/C was carried out using the cooling water drain line in
the cooler of the flammability gas control system, and dry well spray by MUWC
(starting from 7:11 am on the same day), and S/C spray (starting from 7:35 amon the same day) were conducted from time to time to cool the containment
vessel.
Because there was a rising tendency in the pressure of the containment vessel
due to the loss of the heat removal function of the reactor, it was assumed that it
would take time to recover the heat removal function of the reactor, and line
configuration (completing all necessary actions except one last action to open
the outlet valve to the S/C) was conducted for the vent of the containment vessel
between 10:33 am and 10:58 am on the 12th. However, containment vessel ventwas not implemented because the pressure of the containment vessel did notreach the level that would require a vent.

(3) Recovery of residual heat removal system and cold shutdown of reactor
For the restoration works of Unit 2, it was decided to give priority to carrying out
inspection and repair of the pump in the residual heat removal cooling system(B), the seawater pump in residual heat removal system (B), and the coolingpump of the emergency diesel generator (B).
By 11:30 pm on the 13th, temporary cables were laid from the power panel of theradioactive waste treatment building and the power panel of seawater heat40

exchanger building of Unit 3 to connect directly with the motor, and starting from
3:20 am of 14th, pumps started up one by one as soon as they become
available.
At 7:13 am on the 14th, the pump of the residual heat removal system (B) wasstarted. (The plant manager concluded that the situation constituted the end of
the situation of Article 10 of the Special Law for Nuclear Emergency (loss ofreactor heat removal function).)As a result of the continuous cooling of the S/C by the pump of residual heatremoval system (B), the temperature of the S/C gradually declined and fell below
100 C at 3:52 pm on the 14th. (The plant manager concluded that the situation
constituted the end of the situation of Article 15 of the Special Law for Nuclear
Emergency (loss of the pressure suppression function).)In order to cool down the reactor water expeditiously, in addition to the cooling of
the S/C, at 10:48 am on the 14th, the injection of water from the S/C into thereactor from the low-pressure water injection line using the pump of the residual
heat removal system (B) started. At the same time, reactor water was returnedto the S/C via the main steam safety relief valve after cooling down the water in
the S/C using the heat exchanger of the residual heat removal system andreturning it again to the reactor via a low-pressure injection line, making for acircular flow of water (S/C  pump in the residual heat removal system (B) heat exchanger in the residual heat removal system (B)  low-pressure water
injection line→reactor  main steam safety relief valve  S/C), as a temporary
measure.
The temperature of the reactor water dropped below 100C at 6:00 pm of thesame day and cold shutdown was achieved.
At 7:58 am on March 16, about two days after cold shutdown, the monitor of thecontainment vessel observed a rising tendency of hydrogen concentration(Hydrogen Approx.5%, Oxygen Approx. 2%). Therefore, the flammable gas
control system was operated, and hydrogen and oxygen concentration was
successfully controlled below the flammable level of concentration.

4.2.3.4

Situation of Fukushima Daini Unit 3.

(1) From the earthquake to immediately after the arrival of the tsunami
At 2:48 pm on March 11, the reactor automatically shut down and at 3:05 pm, it
was confirmed that it had become subcritical.
Because of the flooding of the seawater heat exchanger building by the tsunami
and from the indications of on/off lamps at the control panel, it was thought thatthe water pump in residual heat removal system (A, C), the seawater pump in
residual heat removal system (A, C) and the cooling pump of emergency diesel
generator (A) were all unable to start up. (At a later date, it was confirmed thatthese failures were caused by the inundation of some of the motors and theemergency low voltage power panel (P/C 3C-2)). Therefore, it became
impossible to start up the pumps in the low pressure core spray system (A) andthe residual heat removal system.
Since the entry of flood water into the seawater heat exchanger building of thisunit was small in relation to that of other units, the impact of flooding on theequipment in the building was not significant and this equipment was considered
to be in usable condition: emergency low-voltage power panel (P/C 3D-2), itsload, water pump for residual heat removal system pump (B, D), seawater pump41

for residual heat removal system pump (B, D), cooling pump for emergency
diesel power generator (B), water cooling pump for diesel power generator forthe high-pressure core spray system, and seawater cooling pump for diesel
power generator for the high-pressure core spray system.
Since there was no flooding from the tsunami on the B2 floor of the reactor
building, pumps in the residual heat removal system (B, C) and high pressure
core spray system were all ready to use.

(2) Injection of water into reactor and cold shutdown
At first, water injection into the reactor was carried out by RCIC but starting from10:53 pm of March 11, alternate water injection by MUWC, which wasintroduced as an accident management measure, was also implemented.
Because of the drop in pressure in the RCIC turbine driving steam due to thedecrease in the reactor pressure, RCIC was manually isolated at 11:58 pm of thesame day by opening the main steam relief safety valve.
Alternative water injection by MUWC was continued thereafter in accordancewith the Emergency Operation Procedure [symptom basis] (EOP).
As a precaution for the contingency of an increase in pressure of thecontainment, line configuration of the containment vent was performed(completing all necessary actions except one last action to open the outlet valve
to the S/C).
At 9:37 am on March 12, the pump in the residual heat removal system (B) was
activated to inject cooling water, and the water temperature of the reactor
dropped below 100C and cold shutdown was confirmed at 12:15 pm on thesame day.

4.2.3.5

Situation of Fukushima Daini Unit 4

The basic operation of Unit 4 is the same as Units 1 and 2. However, in considerationof securing water sources, priority was given to Units 1 and 2 in water injection
operations because their decay heat was more intense. The decay heat of Unit 4 wasconsidered to be less intense, so the water from S/C was injected into the reactor by
HPCS after stirring the water.
(1) From the earthquake to immediately after the arrival of the tsunami
At 2:48 pm on March 11, the reactor automatically shut down and at 3:05 pm on
the same day, it was confirmed that it had become subcritical.
As countermeasures against the tsunami (visual confirmation of the arrival of firstwave at 3:22 pm on March 11), the main steam isolation valve was fully closed
manually at 3:36 pm on March 11 and the depressurization of the reactor wasstarted at 3:46 pm on the same day by the opening of the main steam relief safetyvalve followed by the manual activation of RCIC for injection of water into thereactor,Due to the impact of the tsunami, some of the motors and power panels were
flooded and became unusable. As a result, all of the pumps in the emergency
core cooling system entered a non-bootable state. (At 6:33 pm on the same day,the plant manager determined the situation to be an incident to which Article 10(loss of reactor heat removal function) of the Special Law for Nuclear Emergency
applies.)42(2) Injection of water into reactor and cooling of pressure vessel
At first, water injection into the reactor was carried out by RCIC but after the
automatic isolation of RCIC due to the pressure drop in the RCIC turbine driving
steam at 0:16 am on the 12th, alternate water injection by MUWC was carried out
for the control of the reactor water level.
Starting from 12:32 pm on the 12th, the control of the reactor water level was
conducted by the On/Off of HPCS, which was not impacted by the tsunami andwas available at that time.
The water temperature of the S/C gradually rose due to the operation of RCIC
and the opening of the main steam relief safety valve, and at 6:07 am on the 12th,
the water temperature of the S/C reached above 100C. (The plant manager
determined the situation to be an incident to which Article 15 (loss of pressure
control capability) of the Special Law for Nuclear Emergency applies.)
For the cooling of the S/C, starting from 7:23 am on the 12th, injection of coolingwater (MUWC) to the S/C was carried out using the cooling water drain line in
the cooler of the flammability gas control system, and dry well spray by MUWC
(starting from 7:11 am on the same day) and S/C spray (starting from 7:35 amsame day) were conducted from time to time to cool the containment vessel.
Because there was an upward tendency in the pressure of the containment
vessel due to the loss of the heat removal function of the reactor, it was
assumed that it would take time to recover the heat removal function of thereactor, and line configuration (completing all necessary actions except one lastaction to open the outlet valve to the S/C) was conducted for the vent of thecontainment vessel between 11:44 am and 11:52 am on the 12th. However, thecontainment vessel vent was not implemented because the pressure of thecontainment vessel did not reach the level that would require a vent.

(3) Recovery of residual heat removal system and cold shutdown of reactor
It was decided to give priority to carrying out inspection and repair of pumps inthe cooler of residual heat removal system (B), seawater pump in residual heatremoval system (D), and cooling pump of emergency diesel generator (B). (Themotor of the seawater pump in residual heat removal system (B) was to be
replaced.)
Temporary cables were laid from the power panel of Unit 3 and the powertransformer located near the large equipment entrance of the turbine building ofUnit 3.
At 3:42 pm on the 14th, the pump of residual heat removal system (B) wasstarted. (The plant manager concluded that the situation constituted the end of
the situation of Article 10 of the Special Law for Nuclear Emergency (loss ofreactor heat removal function).)As a result of the continuous cooling of the S/C by the pump of residual heatremoval system (B), the temperature of the S/C gradually declined and dropped
below 100 C at 7:15 am on 15th. (The plant manager concluded that thesituation constituted the end of the situation of Article 15 of the Special Law for
Nuclear Emergency (loss of the pressure suppression function).)In order to cool down the reactor water expeditiously, in addition to the cooling of
the S/C, at 6:58 pm on the 14th, the injection of water from S/C into the reactor
from the low-pressure water injection line using the pump of the residual heatremoval system (B) was started. At the same time, reactor water was returned to43

S/C via the main steam safety relief valve after cooling down the water in S/Cusing the heat exchanger of the residual heat removal system and returning it
again to the reactor via the low-pressure injection line, making for a circular flowof water (S/C  pump in the residual heat removal system (B)  heatexchanger in the residual heat removal system (B)  low-pressure water
injection line  reactor  main steam safety relief valve  S/C), as a temporary
measure.
The temperature of the reactor water dropped below 100C at 7:15 am on the
15th and cold shutdown was achieved.
At 1:21 am on March 17, about two days after cold shutdown, the monitor of thecontainment vessel observed a rising tendency of hydrogen concentration(Hydrogen Approx.5%, Oxygen Approx. 2%). Hence, the flammable gas control
system was operated and hydrogen and oxygen concentration was successfully
controlled below the flammable level of concentration.
4.3 Cooling of spent fuel pool of Fukushima Daini
The temperature of the spent fuel pool of Fukushima Daini Units 1-4 was monitored by
the temperature gauge in the main control room. The temperature gauge of Unit 2,
however, was not functional because the heat sensor tip was exposed out of the water
due to the decreased water level of the pool. Therefore a temporary thermometer was
installed to continue the monitoring.
Because of the loss of the seawater circulation system, it became impossible to deliver
heat from the spent fuel pool to the ultimate heat sink. However, the decay heat of the
spent fuel was not so large, so the rise of the pool water temperature could be
suppressed by circulating the pool water to the cooling system of the pool, which is
powered by the emergency power source. After the recovery of RHR, the temperature of
the pool water was maintained below the limit prescribed by the nuclear facility security
regulations. (The temperature of spent fuel pool water shall be below 65C.)44

5. Analysis of accident response
5.1 Purpose of the analysis of accident response
We believe that we can learn a variety of lessons from the experience of Fukushima Daini,where they were able to swiftly lead the plant to convergence after the devastation of thetsunami. In this aim, we not only took the lessons from the response merely as bestpractices, but also made an in-depth analysis of the accident response.
5.2 Concept of analysis
The INSAG-10 in-depth report on nuclear defense defined the following five levels of
purpose and requirement. (Note 1)
Level 1: Prevention of abnormal operation and failures; Conservative design and highquality in construction and operation.
Level 2: Control of abnormal operation and detection of failures; Control, limiting andprotection systems, and other surveillance features.
Level 3: Control of accidents within the design basis; engineered safety features andaccident procedures.
Level 4: Control of severe conditions including prevention of accident progression andmitigation of the consequences of a severe accident; Complementarymeasures and accident management.
Level 5: Mitigation of the radiological consequences of significant external release ofradioactive materials; Off-site emergency response
Levels 1 to 3 can be achieved through engineered safety features that have been built or
constructed. As such, it is possible to confirm their design capability, such as rated capacity,
by analysis, etc. in the design stage.
However, due to human errors, etc. the actual response after the accident may not be sameas in normal circumstances and the accident may not be handled as intended, or, theanalysis of actual experience in serious accidents that we have encountered will show us
what is important to cope with.
(Note 1: Excerpt from Nuclear Safety Commission reference material "I-Kou-Ki-Gen No. 5-3-2” by
Mr. Masahiro Yamashita, JNES)

In response to the Fukushima Daiichi accident, many companies have been promoting avariety of facility enhancements as permanent or temporary countermeasures, such as theinstallation of embankments and the deployment of power vehicles. As a result, the statusof the equipment of each power plant now differs from that of Fukushima Daini at the timeof the disaster.
In the concept of defense in depth, defensive response to unrecognizable "uncertainties" isrequired based on the "ignore lower level defense" principle. (Please see Note 1 above.)This means that in Level 4 defense, the conditions of engineered safety features to be usedin Level 3 or below may not be assumed. Therefore, support from the internal and external
resources of the power plant to leverage in Level 4 or above (such as use of temporary
equipment or materials, restoration of power supply using off-site cables, and expeditious
recovery of damaged equipment) might be assumed in a variety of patterns.

45

It should be a meaningful exercise to extract factors that can be used as the universal
success factors from these various response patters by analyzing the experience ofFukushima Daini as it can give us lessons that can be utilized in the event of plant accident
with a different design and equipment or in the extreme situation of an accident which has
not been assumed.
5.3 Specific analysis procedures
There is a variety of established methodologies in root cause analysis (RCA) for planningcountermeasures against nonconformity. On the other hand, we don’t see any establishedmethodology for extracting successful factors from the events.
For this reason, we have analyzed the successful factors in the Fukushima Daini response(such as full closure of main isolation steam valve, evaluation of damage to the heatexchanger building, early recovery of emergency pumps, etc.) using the following steps:① Describe the incident.
② Describe the response of Fukushima Daini corresponding to the above based on
the TEPCO accident investigation report.
③ Extract possible mistakes in the above incident and response set by assuming ahypothetical mistake in the response which should result in a mistake in theincident.
④ Analyze and identify the possible factors that could cause such assumed mistakeusing the m-SHEL model, a method for human-factor accident analysis, for eachof the five factors below:m (Management and organization)
S (Software, such as manuals)
H (Hardware, such as machinery)
E (Environment)
L (Live ware, such as yourself and the people around you)
⑤ In reality, at Fukushima Daini, an assumed mistake did not occur because thefactors that might have caused such mistake had been overcome and prevented.
Extract the reason why such mistakes were avoided from the features ofFukushima Daini.
⑥ From among the reasons you extracted, derive the important lessons learned.
The above analysis was carried out for the Unit 1 experience, as a representative.
Fig. 5.3-1 shows the flow of the analysis and Table 5.3-1 shows the results thereof.
① through ⑥ in the attachments correspond to ① through ⑥ above.

46

Time Series

Extraction of Lessons①Occurrenceof incident②Execute
response③Hypotheticalmistake in response③Expectable incident
resulting from the
hypothetical mistake④Estimate possible factors whichcaused the mistake

Progress ofincident④Extract possible factors using the MSHEL model⑤Analyze the reasons why it waspossible to avoid/overcome such possible
factor at Fukushima Daini in considerationof the unique features of Fukushima Daini⑥Extract lessons by analyzing reasonsthat contributed to avoid/overcome thefactorFig. 5.3-1 Flow of analysis

47

Table 5.3-1 result of Analysis of accident response （1/11）

Note: Text written in red is quoted from TEPCO’s report.
Analysis of response at Unit 1(3) Anticipated errors related to response

Date and Time
Date

Time

March 11 14：46(1) Event occurred(2) Response

Description of errors

Events caused byoccurrence of anticipatederrors(5) Reasons why factors of
occurrence of errors could be
prevented or overcome(4) Factors of occurrence of anticipated errors
Category
Management

SoftwareHardwareEnvironment

LivewareOccurrence of supposed
secondary cause(6) Lesson

Description

Occurrence of earthquake
Operators remained waiting low to the ground,with their hands grasping a handrail in front of
the control panel, and, a shift chief
simultaneously made a pre-announcement ofscram operation and directed operators tocommence operations responding to theevacuation operation while waiting for theearthquake tremors to stop (page 136 of
Attachment2).

14：46-• Operator injury due tothe earthquake.
• Operators struck
Failure in operation
operating switches
responding to scramwhen they fell down
due to the earthquake
tremors.

No measures to hold Impossible to holdthe body position
the body position

No.

Since the tremor was very large, Detailed countermeasures otheroperators remained waiting low to than the earthquake-resistantdesign of the main facilities andthe ground with their hands
grasping a handrail in front of the operation procedures are also
effective.
control panel (page 136 of(Handrails in front of the central
Attachment 2).
Operators are routinely trained as control panel, what posture
to how to wait in the event of an operators shall maintain during acontinuous earthquake tremor.)
earthquake.

No.

Furnishings, etc. were fixed,reflecting experience inKashiwazaki (2007 Chuetsu
Offshore Earthquake).

Detailed countermeasures otherthan the earthquake-resistantdesign of the main facilities andoperation procedures are effective(fixing of furnishings, etc.).

No.

The safety system’s earthquakeresistant design worked
effectively.
Training

The earthquake-resistant design
worked effectively (the safetysystem’s earthquake-resistantdesign).

Provision of a hand microphone
as emergency equipment

Detailed countermeasures otherthan the earthquake-resistantdesign of the main facilities andoperation procedures are effective(arrangement of a handmicrophone).

An assistant shift chief used simultaneous
paging to make an announcement to all about
the occurrence of the earthquake andevacuation instructions. Operators at the sitewere communicated to via PHS and were
instructed to evacuate.
14：48

Automatic reactor scram(15:00: It was confirmed that the reactor had notreached criticality (page 136 of Attachment 2))

Operation responding to scram (14:48 ~ )Worsening ofenvironment incentral control roomdue to theearthquake(scattering of
furnishings,
occurrence of
injuries, etc.)

March 11

Damage toequipment necessary
for recovery after
scram due to theearthquake
A shift chief judged that in addition to activationof many alarms, the sound of the fire alarms
was too loud for operators to hear instructions,and gave instructions by means of a handmicrophone which was provided behind theshift-chief’s chair as a piece of emergency
equipment (The fire alarms were later found tobe erroneous.) (page 136 of Attachment 2)

Difficulty ofcommunication
between shift chiefand operators due toactivation of fire
alarms (page 136 of
Attachment 2).

Yes.

Failure in recovery
Failure in core cooling
operations after scram
Following the automatic stoppage of the reactor,
a work management team (a team consisting of
the shift chief and operators, separate from theoperation) working in an office near the central
control room rushed into the central control
room and assisted the shift of operators (page216 of Main Text).

Excessive burdens
placed on operators
in conducting
surveillance of theNo.
plant, judgment of thesituation, operation,communication to
those involved, etc.

No or insufficientpersonnel andframework required
to follow up operators
at the central
operating room48

Burdens were reduced thanks tothe support of the work
management team immediately
after scram.
• The support of the work
management team at the time ofscram is not a necessary
condition to respond to scram.
• The work management team isa team stationed in the room next
to the central control room on a
• What is important is as thedaily shift basis for preparation for
attitude to voluntarily perform
regular inspections such as
whatever necessary, with a strong
preparation of tags.
sense of mission, to make the• It was not obligatory for the teamaccident come to an end.
to support operators at the time ofscram. This team, however,voluntarily provided immediate
support with a firm sense of
mission to protect the plant, taking
advantage of the fact that it
consisted of a shift chief andoperators with corresponding
operational skill.
• It functioned effectively for
restoration.

Table 5.3-1 result of Analysis of accident response （2/11）(3) Anticipated errors related to response

Date and Time
Date

(1) Event occurredTime(2) Response

Description of errors

Events caused byoccurrence of anticipatederrorsCategory
Management

SoftwareHardwareSupport staffs were dispatched from the power
station Emergency Response Headquarters andthe structure was established to enable close
contact between the central control room andthe headquarters so that the operators could
dedicate themselves to the surveillance andoperation of the plant in the response thereafter(page 216 of Main Text).

Upon hearing the announcement of a large
tsunami warning from the power station
Insufficient notification
Emergency Response Headquarters, the shift
on major tsunami
Human damage
chief used simultaneous paging to givewarning to the on-site
emergency evacuation instructions due to thestaffannouncement of a large tsunami warning (page136 of Attachment 2).

(5) Reasons why factors of
occurrence of errors could be
prevented or overcome(4) Factors of occurrence of anticipated errors

Lack or delay ofcommunication of thelarge tsunami
warningannouncement fromthe power station
Emergency
Response
Headquarters to theshift chief, or missingof simultaneous
paging by the shift
chief  possibility ofoccurrence of human
injury.

Paging system failure

Environment

LivewareOccurrence of supposed
secondary cause(6) Lesson

Description

Excessive burdens
placed on operators
in conducting
surveillance of theNo.
plant, judgment of thesituation, operation,communication to
those involved, etc.

Support staffs were dispatchedfrom the power station
Emergency Response
Headquarters and a structure wasestablished to enable close
Importance of backup in order forcontact between the central
operators in the central control
control room and theroom to dedicate themselves toheadquarters, while operators
operation.
were able to dedicate themselvesto the surveillance and operationof the plant in the response
thereafter (page 216 of Main
Text).

No.

It was expressly stated that
Detailed countermeasures othersimultaneous paging should bethan the earthquake-resistantmade at the time ofannouncement of a large tsunami design of the main facilities andoperation procedures are effective
warning.
(simultaneous paging of the large
Desktop exercises such as
regular review of procedures were tsunami warning).
conducted.

No.

It is important to establish in
Since the Iwaido Line, like theadvance a structure which allows
power station, is property offor swift support from any
TEPCO, the situation of the powerorganization outside the power
station could be quickly sharedstation (advantage of vertical(advantage of vertical integration
integration of generation andof generation and transmission).
transmission).

No.

Observation by means of on-site
surveillance camera

The Emergency Response Headquarters fordisasters had been established in the head
office (page 126 of Attachment 2).

15：06
Offsite power situation

14：48

Shutdown of one (1) line of
the Tomioka Line (page136 of Attachment 2)

One (1) line of the IwaidoLine was shut down due toequipment faults in ShinFukushima Substation(page 136 of Attachment2). There were a total offour (4) lines as offsite
power; two (2) lines of the
Tomioka Line (500kV) andtwo (2) lines of the IwaidoLine (66kV). One (1) line of(15：50)the Iwaido line had been ina planned outage prior to
the earthquake, and thetwo (2) lines of the
Tomioka Line were shut
down after the earthquake,and then power wascontinuously received fromthe Tomioka No. 1 Line
(page 136 of Attachment
2).
On the Iwaido Line, one (1)(March 12) (13：38) line was restored (page136 of Attachment 2).
On the Iwaido Line, one (1)(March 13) (5：15) line was restored (page136 of Attachment 2).

Delay in early
restoration of the
Iwaido Line

Delay in preparation
Continuous situation of of personnel,
less reliable offsite power equipment andsupply with only one (1) materials, etc. forrestoration of theline.
Iwaido Line.

Responsive operation immediately after the arrival of the tsunami

March 11 15：22

The fact that a large
Observation of the firsttsunami has struck or
It was observed by an on-site surveillance
wave of the tsunamithat damage to
Delay in response
camera that the tsunami was progressing(thereafter, the tsunami
equipment could havethereafter
was intermittently observed toward the breakwater (page 137 of Attachment
been caused by large
2).
until 17:44 (page 126 oftsunami was not fully
Attachment 2).
recognized.

Visual means forobservation is notavailable.

49

Importance of means of observing
damage situation

Table 5.3-1 result of Analysis of accident response （3/11）(3) Anticipated errors related to response

Date and Time
Date

Time

(1) Event occurred(2) Response

Description of errors

Events caused byoccurrence of anticipatederrors(5) Reasons why factors of
occurrence of errors could be
prevented or overcome(4) Factors of occurrence of anticipated errors
Category
Management

SoftwareHardwareEnvironment

LivewareOccurrence of supposed
secondary cause(6) Lesson

Description

While continuing to perform surveillance mainly
Surveillance of planton the reactor system control panel, a shiftconditions was possible
chief, taking the consequences of the tsunami
because approximately half
into consideration, placed operators at theof the instruments andcontrol panels where the operation condition oflamp indicators forseawater system components (seawater intake
surveillance of parameters
pumps and cooling water pumps), which are
and observation ofimportant for reactor heat removal, could be
operation condition wereobserved and instructed them to reportsecured (page 137 of
information as appropriate (page 137 of
Attachment 2).
Attachment 2).
With regard to emergency
component cooling system
pumps, stoppage of
operating pumps was
confirmed by means ofoperation/stop lamp
indicators, etc. (page 137
of Attachment 2).

Omission or delay in
In accordance with tsunami response
procedures (page 137), circulation water pumps conducting manualstop of circulation
were manually stopped (page 126 ofwater pumps
Attachment 2).

15：33

15：34

Omission ofoperation by shiftoperators

No.

• CWP stop was described in thetsunami response operation
procedures.
The procedures prepared and• Since operators were familiar
training conducted in advancewith the tsunami response
functioned effectively.
operation procedures, they wereable to perform operations
properly.

Emergency diesel
generators (A), (B) and (H)were automatically started
and, immediately
thereafter, wereautomatically stopped as aconsequence of thetsunami (page 126 of
Attachment 2).
Lowering of reactor waterlevel due to continuous
leakage of steam from areactor to a condenser
Unavailability of RCIC
due to drop of reactor
pressure

15：36

Since main steam condensation by condensers
Omission or delay in
had become impossible (page 137 of
conducting MSIV fullAttachment 2), MSIVs were fully closed byclosemanual operation (page 126 of Attachment 2).

15：36

The reactor core isolation cooling (RCIC)
Omission or delay insystem was manually started (thereafter
conducting manual
start/stop occurred as appropriate) (page 126 ofstart of RCIC
Attachment 2).

15：55

Depressurization of reactors (safety relief
valves (SRVs) open) was started (thereafter
core pressure was controlled by repeated open
/shut) (page 126 of Attachment 2). Control ofCore damage due toFailure to maintainreactors’ water level and pressure
reactor water level due failure to maintain reactor(depressurization) was conducted by using
to an operational error water level
relevant parts of emergency operation
procedures (EOP) [symptoms basis] (page 137
of Attachment 2).
Reactor water level was maintained by RCIC
(page 220 of Main Text).

50

Omission or delay inconducting MSIV full- No.
close• Description in procedures• Training

The procedures prepared andtraining conducted in advancefunctioned effectively.

Omission or delay inconducting start of
No.
RCIC

• Description in procedures• Training

The procedures prepared andtraining conducted in advancefunctioned effectively.

Operational error

Procedures (EOP) (page 137 of
Attachment 2)
Training

The procedures (EOP) preparedand training conducted in advancefunctioned effectively (maintaining
reactor water level,
depressurization and transfer toalternative water injection).

No.

Table 5.3-1 result of Analysis of accident response （4/11）(3) Anticipated errors related to response

Date and Time
Date

Time

15：57

(1) Event occurred(2) Response

Description of errors

Events caused byoccurrence of anticipatederrors(5) Reasons why factors of
occurrence of errors could be
prevented or overcome(4) Factors of occurrence of anticipated errors
Category
Management

SoftwareHardwareEnvironment

LivewareOccurrence of supposed
secondary cause(6) Lesson

Description

Circulation water pumps(A) and (B) wereautomatically stopped(page 126 of Attachment
2).

Maintaining of reactor water level and cooling of containment vessel
As it was not possible to start the residual heatremoval (RHR) system, which has functions to
inject water to cool reactors and for heatremoval after the depressurization of a reactor,
because emergency component cooling system
pumps were unavailable as a consequence ofthe tsunami, in order to prepare for water
injection cooling to reactors after stopping
Configuration of
RCIC, preparation of an alternative water
alternative water
injection by means of make-up water
injection by means of Core damage due tocondensate (MUWC) system, which had been
MUWC could not have failure to maintain reactor
introduced as an accident management (AM)been completed before water levelmeasure, was commenced (page 137 of
RCIC became
Attachment 2).
unavailable.
Because the power to drive valves necessary
for configuration of line was lost as aconsequence of the tsunami, manual opening
operation was conducted on site. Afterconfiguration of line was completed, injection
valves were opened from the central control
room, and then water injection capability wasconfirmed (page 138 of Attachment 2).

March 11

17：35

Because the possibility of reactor coolant
leakage in reactor containment vessels could
not be denied, it was judged that the specified
event pursuant to Item 1 of Article 10 of the Act
on Special Measures Concerning Nuclear
Emergency Preparedness had occurred, andaccordingly, it was reported to the competentauthorities, etc. at 17:55.
It was later judged that it did not correspond tosuch specified event (page 126 of Attachment
2).

17：53

The drywell (D/W) cooling system was manually
started (page 126 of Attachment 2).
With the expectation of causing suppression
against the pressure increase of PCV, D/W
cooling system (no cooling source) was
D/W cooling system is
manually started. A drop in D/W temperatureunavailable due to loss
was observed immediately after the start, andof offsite power.
this information was reported to the Unit 3 andUnit 4 shift chiefs. Following this, said shift
chiefs conducted similar response andobserved a drop in D/W temperature (page 138
of Attachment 2).

18：33

Because of the failure to start the facility with thereactor heat removal function, it was judged thatthe specified event pursuant to Item 1 of Article
10 of the Act on Special Measures Concerning
Nuclear Emergency Preparedness had
occurred and accordingly, it was reported tocompetent authorities, etc. at 18:49 (page 126
of Attachment 2).

Description of line
configuration is notarranged as in theprocedures.

Loss of offsite power

Alternative water injection bymeans of MUWC, which had been
introduced as an accident
management measure, functioned
effectively.

No.

Line AM guidance procedures
prepared as a measure against
AM

No.

Offsite power was available.

No.

• It remained free fromearthquake damage thanks to theresistance capability of equipmentof MUWC, which was used for AM The earthquake-resistant design
but whose category offunctioned effectively.
earthquake-resistant design was (Earthquake-resistant capability ofclassified as base load system.
base load equipment)• Since offsite power wasavailable, it was possible to use
MUWC.

By means of SRV, reactor pressure was
gradually decreased to such pressure level thatwater injection by MUWC became possible(page 220 of Main Text).

March 12 0：00

3：50

Alternative water injection by means of MUWC
was started (page 127 of Attachment 2). Water
injection to reactors using a combination of
MUWC is unavailable.
RCIC and MUWC was started (page 216 ofMain Text)

Damage to MUWC
system due toearthquake

Fast depressurization of reactors was started(page 127 of Attachment 2).

51

Loss of offsite powerTable 5.3-1 result of Analysis of accident response （5/11）(3) Anticipated errors related to response

Date and Time
Date

Time

(1) Event occurred(2) Response

Description of errors

Events caused byoccurrence of anticipatederrors

4：56

Fast depressurization of reactors wascompleted (page 127 of Attachment 2).

4：58

RCIC was manually isolated in order todecrease steam pressure to drive the RCIC
turbine in association with reactor pressure drop
while maintaining conditions under which it waspossible to maintain the reactor water level by Occurrence of blankperiod during whichMUWC (page 220 of Main Text).
Core damage due towater level could not
As a result, it was possible to maintain the
failure to maintain reactor
reactor water level as high as the normal water be maintained by RCIC
water level
level and switch-over to water injection by low or MUWC due to an
operational errorpressure system could be made seamlessly(page 220 of Main Text).
After this, the reactor water level was controlled
only by MUWC (page 127 of Attachment 2)(page 216 of Main Text).

5：22

Because temperature and pressure in
suppression chamber (S/C) rose due to RCIC
exhaust and reactor depressurization by SRV(page 127 of Attachment 2) and thetemperature in S/C rose to no less than 100C,
it was judged that this was an event to which
Article 15 of the Act on Special Measures
Concerning Nuclear Emergency Preparedness(loss of suppression function) applies (page 217
of Main Text).

6：20

The power station Emergency Response
Headquarters investigated measures andmethods for cooling of S/C. A shift chief
instructed operators to utilize the discharge linefrom FCS coolers to S/C and conduct cooling of
S/C by MUWC or MUWP in accordance with the
instructions given by the headquarters (page138 of Attachment 2).
S/C cooling was conducted by using flammablegas control system (FCS) cooling water(MUWC) (page 127 of Attachment 2).

Drywell spray was conducted using MUWC
Omission or delay in(thereafter conducted as appropriate) (page 127 conducting drywellof Attachment 2).
spray

7：10

(5) Reasons why factors of
occurrence of errors could be
prevented or overcome(4) Factors of occurrence of anticipated errors
Category
Management

SoftwareHardwareEnvironment

LivewareOccurrence of supposed
secondary cause(6) Lesson

Description

No.

• Procedures were well prepared.
• Procedures prepared and• Training was conducted.
training conducted in advance• Personnel were dispatched andfunctioned effectively.
assigned to communicate with the• Importance of backup so that
Emergency Response
operators in the central control
Headquarters so that shiftroom can dedicate themselves tooperators could dedicate
operation.
themselves to operation.

Reaching maximum
operating pressure of
Hesitating to conduct
drywell due to omission
drywell spray fromof temporary suppression
the viewpoint ofof temperature andproperty protection
pressure, or conducting
containment vessel ventNo.

The sense of making safety the
first priority was thoroughly kept inmind.

Oversight of D/W
and/or S/C spray
operation by means
of MUWC

No.

Procedures were reflected in
EOP.
Training

An operational error

Alternative water injection to reactors by MUWC
was switched to drywell spray and S/C spray as
appropriate and efforts to suppress PCV
pressure increase were conducted (page 138 of
Attachment 2).
Drywell and S/C spray by means of MUWC was Oversight of D/W
introduced as one of measures for accident
and/or S/C spraymanagement and reflected in EOP (page 217 of operation by means ofMain Text).
MUWC
S/C spray was conducted using MUWC (page127 of Attachment 2).

7：37

7：45

The Prime Minister directed
people in the zone within 3
km from the power station
to evacuate and people in
the zone within 10 km
therefrom to remainindoors (page 127 of
Attachment 2).

7：45

S/C cooling using FCS
cooling water was stopped(page 127 of Attachment
2).

52• Procedures prepared in advancefunctioned effectively.

Table 5.3-1 result of Analysis of accident response （6/11）(3) Anticipated errors related to response

Date and Time
Date

Time

(1) Event occurred(2) Response

Description of errors

Events caused byoccurrence of anticipatederrors(5) Reasons why factors of
occurrence of errors could be
prevented or overcome(4) Factors of occurrence of anticipated errors
Category
Management

SoftwareHardwareEnvironment

LivewareOccurrence of supposed
secondary cause(6) Lesson

Description

Preparation of PVC pressure-proof ventConfiguration of PCV pressure-proof vent-line
was commenced (page 127 of Attachment 2). In
contrast to containment vessel pressure-proof
vent after core damage under accident
management, this is done for the purpose of
decreasing pressure that has risen incontainment vessels by releasing steam, etc.
through pools in suppression chambers while
maintaining the integrity of the core throughcontinuous water injection to reactors in thecase that there is delay in restoration of reactor
heat removal function (page 217 of Main Text).

March 12 10：21

It was recognized by the power station
Emergency Response Headquarters that PCV
pressure tended to rise because the plantparameters, such as reactor water level andD/W pressure, could be obtained throughcommunication with the central control room(PHS) (page 139 of Attachment 2).

Delay incommencement of
preparation for vent・Cannot recognizethat preparation for
Vent cannot bevent takes muchconducted whenmore time thannecessary.
expected.
(As for results, it never・Cannot understandreached the pressure
under which vent should the risk resulting fromthe delay of RHR
have been required.)recovery efforts.

Delay of RHR
recovery efforts

Anticipating that it would take time to restore
reactor heat removal function, it was determinedthat configuration of the line for the PCV
pressure-proof vent (the condition that one
action of opening operation an exit valve at S/Cside remained untaken) should be conducted(page 139 of Attachment 2).
Because the power for pressure-proof vent-line
inlet valve- (air controlled valves) driven
electromagnetic valves for air control was lost,the opening operation could not be conducted.
The power station Emergency Response
Headquarters, therefore, investigatedcountermeasures (a method of connecting asmall cylinder directly to the valve driving part ora method of performing the opening operation
by restoring power to such electromagnetic
valve), judged that there should be a time
margin in view of the trend of PCV pressure
rising, and determined that the opening
operation should be conducted by restoring
power to such electromagnetic valve (page 139
of Attachment 2).

14：05

It was confirmed that the
government’s evacuation
action of evacuatedresidents had been
completed.

17：39

The Prime Minister directed
the population in the zone
within 10 km from
Fukushima Daini Nuclear
Power Station to evacuate(page 127 of Attachment
2).
Configuration of PCV pressure-proof vent-line
was completed (page 127 of Attachment 2).

18：30(March 13)

Drywell pressure was
gradually rising due to lossof the function to remove
heat from reactors, and it
reached design pressure(0.38 MPa [abs]) on thethird day, but neverreached maximum
operating pressure (0.41
MPa [abs]) (page 220 ofMain Text).

53

No.

・Because preparation for venttook much more time than
expected at the Fukushima Daiichi
nuclear power plant, the head
office recommended earlier
Importance of establishing a plan
preparation for vent. The
with foreseeability.
Headquarters at 2F was also
aware of the necessity of ventpreparation.
・RHR recovery efforts wentsmoothly.

Table 5.3-1 result of Analysis of accident response （7/11）(3) Anticipated errors related to response

Date and Time
Date

Time

(1) Event occurred(2) Response

Description of errors

Events caused byoccurrence of anticipatederrors(5) Reasons why factors of
occurrence of errors could be
prevented or overcome(4) Factors of occurrence of anticipated errors
Category
Management

SoftwareHardwareEnvironment

LivewareOccurrence of supposed
secondary cause(6) Lesson

Description

Restoration of residual heat removal system

The power station Emergency Response
Headquarters examined the situation of damage Omission of prioritizing Delay in restoration ofplant, which is of highto the facility through site observation and made restoration works
prioritya plan for restoration strategy and prioritization among units
of works (page 217 of Main Text).

(March 11)

Failure to perform
prioritization

The plant data which had been
regularly collected by the central
control room were arranged into
trends by the Emergency
Importance of early planning andResponse Headquarters,arrangement of materials based
containment vessel pressure
rising trends were monitored, the on site observation.
time when rupture disk pressure
would reach setting pressure wasestimated, and then prioritization
among units was determined.

No.

It was, however, unable to dispatch a
restoration team to the site immediately
because the situation of the site was such thatno lighting was available, extensive debris andopenings posed danger, the paging system
could not be used as a means ofcommunication for evacuation at the time oftsunami striking under continuous
announcement of after-shocks and large
tsunami warnings and in addition, PHS could not
be used in the buildings damaged by thetsunami (page 217 of Main Text).
During site observation at Hx/B, desperate
efforts to examine the damage situation were
Further delay in sitemade, relying only on a small number ofobservation
flashlights available in the unlit darkness, being
submerged into pool of water made by thetsunami and clearing over debris and waste,and, repeatedly evacuating to high ground at
every after-shock while tsunami warnings were
continuously announced (page 139 of
Attachment 2).

(Around
22:00)March 12

Delay in establishing a
restoration plan due todelay in observation ofsite situation

Means ofcommunication
unavailable at site.

• No lighting at site
• Dangerous
Fear of the tsunami
environment due tostriking again duringexistence ofsite observation
extensive debris andopenings

Yes.

• Importance of overcoming fearwith a strong sense of mission to
restore after an accident• Sense of responsibility• Establishment ofovercoming fear
countermeasures and an• A means to communicate about implementation structure to
perform the countermeasures bysheltering was established byarranging messengers according the power station Emergency
Response Headquarters
to circumstances, etc.
according to circumstances• Preparation of portabletemporary lighting

It was around 22:00 on March 11 when arestoration team commenced examination of
the damaged site, such as a seawater heatexchanger building near the sea coast, etc. after
having established a means of communication,using messengers, with regard to sheltering andhaving prepared safety equipment.

Based on site examination results given by the
restoration team (conditions of equipment andsituation of flooding of power system (page 139
of Attachment 2)), the power station Emergency
Response Headquarters determined the policythat priority should be given to conducting• Fault in observation
restoration works for residual heat removal
component cooling pump (D), residual heatof site situation
removal seawater pump (B) and emergency• Omission ofdiesel generator facility cooling system pumpprioritizing restoration(B) in the seawater heat exchanger building
works(page 217 of Main Text).
Regarding residual heat removal component
cooling pump (D) and emergency diesel
generator facility cooling system pump (B), thepolicy that motors should be replaced wasdetermined (page 217 of Main Text).

Delay in restoration
works due toestablishment of anincorrect wrong
restoration policy

Urgent procurement of motors was requested to
Kashiwazaki Kariwa Nuclear Power Station.
Delay in support from
Kashiwazaki Kariwa Nuclear Power Station
the side of
Delay in restoration
gave proactive assistance in procuring the
Kashiwazaki Kariwa
equipment and materials required by Fukushima
Nuclear Power Station
Daiichi and Fukushima Daini Nuclear Power
Stations (page 217 of Main Text).

Omission ofprioritizing restoration
works due toabsence ofgovernance of thepower station
Emergency
Response
Headquarters• Deterioration ofenvironment of thelocation of the power
station Emergency
Response
Deficiency in skills to
Headquarters
observe the situationNo.
(scattering ofof the facility infurnishings, etc.)
question• Failure to take out
drawings to be used
for restoration works
as a consequence ofthe earthquake

Delay in establishingcooperation acrossorganizations

Poor communication
for mutual
understanding
betweenNo.
organizations(communication formutual confirmationof usable motor
models, etc.)

54•Available equipment (pumps)
was selected based on the resultsof site observation, and theseresults were indicated in a matrix, • Importance of sharing
and priority equipment to be
information
repaired in order to restore the• Importance of the power station
heat removal function wereEmergency Response
selected.
Headquarters grasping the• Adequate judgment of the power situation (situation of damage toequipment)
station Emergency Response• Importance of the power station
Headquarters• Routine skill concerning repair of Emergency Response
Headquarters establishing ansuch facility
adequate response strategy
・The seismic isolation building
was effective although it lost the (prioritization of restoration)
power for 2 to 3 hours due to the • The important anti-seismicbuilding functioned effectively.
tsunami.
• Careful consideration with regard• Countermeasures had beentaken for racks for documents in to earthquakes is effective (fixing
an office building based on thefurnishings, etc.)
experiences of the 2007 Chuetsu
Offshore Earthquake, anddocuments could be taken out.

Kashiwazaki Kariwa Nuclear
Power Station, which is anorganization within the same
company, also participated in avideo conference and shared thesituation of Fukushima Daini.

Importance of establishing in
advance a structure to allow for
swiftly receiving support fromoutside of the power station(Importance of sharing thesituation in order to swiftly receivenecessary support from the othernuclear power stations)Table 5.3-1 result of Analysis of accident response （8/11）(3) Anticipated errors related to response

Date and Time
Date

Time

(1) Event occurred(2) Response

Description of errors

Events caused byoccurrence of anticipatederrorsRegarding motors for some of the emergency Delay in orders of
motors from
Delay in restoration
component cooling system pumps of Unit 1,
insulation resistance could not be recovered in manufacturers
spite of cleaning the motors. Therefore, motors
were transported from Mie Prefecture to
Fukushima Airport by a Self Defense Forcestransport plane. As soon as they arrived at thesite, installation and connection with temporary
cables were commenced immediately and werecompleted by the evening of March 13 (page
Delay in transportation
Delay in restoration
140 of Attachment 2).
of motors

The power station Emergency Response
Headquarters requested from the head office
the urgent procurement of high voltage powersource cars, portable transformers and cables
Delay in support fromin order to connect motors with power panels
the side of the headremaining free from the consequences of theofficetsunami and power source cars, because power
panels supplying power to motors of pumps had
lost function due to flooding (page 217 of Main
Text).
Among the power panels which were available
and remained free from the consequences of
the tsunami, it was determined that a power
panel in a radioactive waste treatment building
should be used. The reason why the panel in theradioactive waste treatment building, which was
the farthest from the seawater heat exchanger Selection of otherbuilding, was chosen was that since there would routing for cabling
be fewer complicated cabling works and most works
routing would run on the ground along a straightroad, it would be appropriate for laying heavy
and hard cables manually. This was the
judgment made by a restoration team based on
the actual situation of the site (page 218 of Main
Text).

Delay in restoration

Delay in restoration of
power

Category
Management

SoftwareHardwareEnvironment

Delay in locating
motorsDelay in response bycontractors

Delay in long
distance (from Mie
Prefecture to
Fukushima)transportation due todeterioration of roadtraffic conditions due
to earthquake
damageDelay in establishingcooperation acrossorganizations

Poor conduct intaking up the opinionsof each teammember within the
team

The equipment and materials which the head
Unavailability of a
office had been requested to procure arrived
one after another at Fukushima Daini by around driver for a large trailer
6:00 on March 13. Incidentally, transportation to transport heavy
took longer than expected as a consequence of cargoes to the power
mobile phones being unavailable between the station, includingcargoes from places
power station Emergency Response
Headquarters and the transportation team, etc. other than Kashiwazaki(page 218 of Main Text).
It was decided that temporary cables would betransported from outside by helicopter. It was
hurriedly decided that a field or a baseball fieldwould be used as a heliport, and works to
prepare to receive cargo were conducted• Delay in preparing toovernight; the fence around the baseball ground
Delay in restoration ofreceive, such as
was removed before dawn on March 12 andpower
guiding lighting, etc.
twenty (20) cars owned by employees werearranged for lighting to guide helicopter landing.
Under bad road conditions resulting from theearthquake, car transportation was also
arranged (page 139 of Attachment 2).

(5) Reasons why factors of
occurrence of errors could be
prevented or overcome(4) Factors of occurrence of anticipated errors

Delay in establishingpreparedness toreceive, such as
guiding lighting, etc.

LivewareOccurrence of supposed
secondary cause

Description

No.

Importance of establishing in• A procurement list had been
advance a structure to allow for
prepared in advance.
swiftly receiving support from
• Good business relationships hadoutside of the power station
been established; even though(Preparation of procurement
requests were only made bysources of necessary equipment
telephone, contractors madeand materials and information
quick responses favorably.
about availability in advance)No.

• Transportation by a SelfDefense Forces transport plane• The head office’s Emergency
Response Headquarters fordisasters made a request to the
Self-Defense Forces.

Importance of establishing in
advance a structure to allow for
swiftly receiving support fromoutside of the power station(Importance of swift support ofgovernment organizations)

Poor communication
for mutual
understanding
betweenorganizations
No.
(communication formutual confirmationof necessary
equipment andmaterials, etc.)• The head offices’ Emergency
Response Headquarters fordisasters also had control overorganizations within the same
company outside the nuclear
power division (advantage ofvertical integration of generationand transmission).
• Corporate-wide emergency
response manual

Importance to establish inadvance a structure to allow for
swiftly receiving support fromoutside of the power station(Advantage of utilities vertical
integration of generation andtransmission)

No understanding ofactual situation ofNo.
manual cabling works

There was the capability torespond according tocircumstances to such
unexpected events, such as thecase of manual cabling works.
• Understanding of cabling works
obtained through routine
maintenance• Calm judgment within the team

Importance of establishing anadequate response policy• (Proper selection of routing forcabling works)• (Adequate judgment made by aleader of the power station
Emergency Response
Headquarters based on proper
implementation of function byeach team and information and/or
opinions properly taken up fromeach team)Refusal by drivers ofcompanies to whichtransportation wasPartially occurred.
outsourced to enter
the controlled
evacuation area

• Appointment of drivers with• Transportation by drivers withlicenses for large vehicles aslicenses to drive large vehicles
emergency personnel
belonging to TEPCO subsidiaries• Advance preparation of aand subcontractors working in the
structure to allow for receiving
power station
support from the Self-Defense• Transportation by governmental
Forces and so on more thoroughly
emergency response(preparatory radioactive education
organizations such as Selfto be provided for Self-Defense
Defense Forces
Forces personnel, etc.)

No.

The total length of temporary cables amounted
to as much as 9 km for the four units of theplant. Laying works for these cables werecompleted manually by as many as 200
personnel, including employees from the
distribution division and workers of
subcontractors no later than around 23:30 on
March 13 (page 218 of Main Text).

Governance of the power station
Emergency Response
Headquarters functioned
effectively.

• Head office Emergency
Response Headquarters had
control over divisions other than
Nuclear Power Division in thesame company (advantage ofvertical integration of utilities).
• Mass procurement of cables,55(6) Lesson

Establishment of a plan for
countermeasures according tocircumstances in line with thesituation of the site and astructure for the implementation of
the countermeasures

Table 5.3-1 result of Analysis of accident response （9/11）(3) Anticipated errors related to response

Date and Time
Date

Time

(1) Event occurred(2) Response

Description of errors

For the cabling works, several combined teams
consisting of 40 personnel including employees
and workers of on-site subcontractors as well as
personnel from the distribution division of eachbranch office (employees and subcontractors)
were formed, and works were conducted asafter-shocks occurred and debris was scatteredaround as a consequence of the tsunami. The Necessary workers
works were conducted at nighttime, relying on cannot be arranged.

Events caused byoccurrence of anticipatederrorsDelay in restoration ofpowerhead lights since it was completely dark (page140 of Attachment 2).

Temporary cables were made up of a packageof three (3) 2-3 cm thick wires twisted, and one(1) 200 m long cable weighed no less than 1 t.
It was required that the cable be laid as long as
approximately 800 m from the RW building to
Hx/B. Under normal conditions, the work shouldhave been conducted by machine over thecourse of several days; this time, however, theworks were conducted manually at a very highpace and the cabling work for total extension of
approximately 9 km was partly completed on
March 12 and mostly completed on March 13(page 140 of Attachment 2).

Based on continuous surveillance andestimation of plant data (containment vesselpressure) made by a technical team of thepower station Emergency Response
Headquarters, first priority was originally given
to the cabling work for Unit 2, of whichcontainment vessel pressure had been rising
fastest. Since, however, it was discovered
before dawn on March 13 that the containment
vessel pressure of Unit 1 was rising faster thanthat of Unit 2, the priority of cabling work waschanged to Unit 1 (page 218 of Main Text).

• Omission of
Unit 1 drywell pressure
prioritization of cablingreaches maximum
works among units
operating pressure, or• Mistake in selection
containment vessel ventof priority unit for
shall be conducted.
cabling works

Observation of condition of mechanical parts forpumps and installation of motors wereDelay in works
conducted in parallel with the cabling works(page 218 of Main Text)

Delay in restoration(5) Reasons why factors of
occurrence of errors could be
prevented or overcome(4) Factors of occurrence of anticipated errors
Category
Management

Software• Divisions other thanthe Nuclear Power
Division refuse todispatch personnel tothe site where
nuclear disaster has
occurred, •Subcontractors
hesitate to dispatch
their employees tothe nuclear
emergency
evacuation area.

HardwareNecessary stock ofequipment andmaterials is notavailable.

Environment

LivewareOccurrence of supposed
secondary cause

Dispatched personnel
refuse to enter thesite declared aNo.
nuclear emergency
evacuation area.

(6) Lesson

Description
etc. was possible as the company
was a vertically integrated electric
power company including
distribution and construction• Importance of establishing indivisions.
advance a structure to allow for• Company loyalty: Divisions otherreceiving swift support fromthan the Nuclear Power Divisionorganizations outside the power
had a strong will to stop thestation (advantage of utilities with
nuclear disaster.
respect to vertical integration of• The subcontractors’ sense thatgeneration and transmission).
the plant belonged to them
• Importance of establishing a(preparedness of on-siteroutine relationship with on-site
subcontractors stationed at thesubcontractors who provide
power station)
cooperation in case of emergency• Regarding requests tocontractors for restoration works,
the head office’s Procurement
Department had madeagreements with contractors andmanufacturers concerning support
and cooperation in case of“emergency disasters” and“emergency events.” Within thisframework, special cooperation
could be requested.

Omission ofprioritization of
cabling works among A team in charge ofunits due to absence surveillance andof governance in the estimation of plantdata is not clearly
power station
identified.
Emergency
Response
Headquarters

Importance of the power station
Emergency Response
Headquarters establishing an• Governance of the power station
adequate policy for response
Emergency Response• (Prioritization of cabling works
Headquarters
among units)• Clear identification of division of• (Adequate judgment made by a
the roles and tasks to beleader of the power station
performed by each team
Emergency Response(technical team) of the power
Headquarters based on proper
station Emergency Response
implementation of function by
Headquarters
each team, and information and/or
opinions properly taken up fromeach team)

Necessary personnel
cannot be arranged.

• According to the manual for
emergency disaster preventive
activities, food for 250 personnel
for three (3) days and drinking
water for 50 days. In addition,
food for shift operators for 40days and food for 60% of officepersonnel for two (2) weeks had
been stocked ascountermeasures against• Necessity to stock appropriate
influenza A (H, N). This food was amounts of food and drinking
distributed to personnel at thewater
power station at the time of the• Importance of establishing aearthquake disaster, and as aroutine relationship with on-site
result, demand was filled for three subcontractors who provide(3) days. On March 13, support
cooperation in case of emergency
goods from the other branch
offices arrived at the power
station.
• Preparedness of on-site
subcontractors stationed at thepower station• Maintenance of each piece ofequipment had been continuously
ordered from the same company.

Not only personnel
for emergency
response consistingof employees (200
employees) but also
substantially almost
all employees(approximately 400
employees) andmany of theNo skill for the works No.
subcontractors’
employees(approximately 1,900
employees) remainedat the power stationfor emergency
response. Therefore,
there was a greater
shortage of rations
for personnel than
expected.

56

Table 5.3-1 result of Analysis of accident response （10/11）(3) Anticipated errors related to response

Date and Time
Date

Time

(1) Event occurred(2) Response

March 13 20：17

Residual heat removal component coolingseawater pump (B) was manually started (page127 of Attachment 2).

21：03

Residual heat removal component coolingseawater pump (D) was manually started (page127 of Attachment 2).

March 14 1：24

Residual heat removal (RHR) system pump (B)was manually started (S/C cooling mode wasstarted). Residual heat removal component
cooling seawater pump (B) was manually
started.
It was judged that the occurrence of thespecified event pursuant to the Act on Special
Measures Concerning Nuclear Emergency
Preparedness should be called off (page 127 of
Attachment 2).

1：44

Emergency diesel generator facility coolingsystem pump (b) was manually started.
Residual heat removal component coolingseawater pump (B) was manually started (page127 of Attachment 2).

3：39

RHR (B) spray mode was started.
Residual heat removal component coolingseawater pump (B) was manually started (page128 of Attachment 2).

10：05

Water injection to reactors by RHR (B) low
pressure water injection mode was conducted(page 128 of Attachment 2)
While injection of water in suppression
chambers to reactors via low pressure water
injection line by RHR pump (B) was started inorder to perform early cooling of reactor water in
addition to cooling of suppression chambers,
reactor water was made to flow into
suppression chambers via main steam safety
relief valves, and emergency cooling measures
were taken using the line where water insuppression chambers was cooled by RHR heatexchanger (B) and was injected to reactors
again via a low pressure water injection line
(S/C  RHR pump (B)  RHR heat exchanger(B)  low pressure water injection line reactor  SRV  S/C).

10：15

Since the temperature of S/C dropped to lessthan 100°C, it was judged that the specified
event pursuant to Article 15 of the Act on
Special Measures Concerning Nuclear
Emergency Preparedness could be cancelled.
Accordingly, it was reported to authorities, etc.
at 10:35 (page 128 of Attachment 2).

17：00

Reactor water temperature dropped to less than
100°C and reactor cold shutdown was achieved(page 128 of Attachment 2).

March 16 5：12

As containment vessel atmosphere monitoring
showed a trend of Hydrogen concentration
increase (Hydrogen approximately 5%, Oxygen
approximately 2%), the flammable gas
concentration control system was operated. The
concentration of Hydrogen and Oxygen was
controlled well to prevent them entering into theflammable range (page 128 of Attachment 2).

Description of errors

Events caused byoccurrence of anticipatederrors(5) Reasons why factors of
occurrence of errors could be
prevented or overcome(4) Factors of occurrence of anticipated errors
Category
Management

Software57

HardwareEnvironment

LivewareOccurrence of supposed
secondary cause

Description(6) Lesson

Table 5.3-1 result of Analysis of accident response （11/11）(3) Anticipated errors related to response

Date and Time
Date

Time

(1) Event occurred(2) Response

Description of errors

Events caused byoccurrence of anticipatederrors(5) Reasons why factors of
occurrence of errors could be
prevented or overcome(4) Factors of occurrence of anticipated errors
Category
Management

SoftwareHardwareEnvironment

LivewareOccurrence of supposed
secondary cause

Description

The increase of Hydrogen concentration isconsidered as follows:
It is possible that before cold shutdown, anoxidization reaction of zinc (paint, etc.) and soon in the containment vessel could haveoccurred under conditions of radiolysis and hightemperature and humidity. It is also considered
to be possible that after the cold shutdown, anoxidization reaction of zinc and so on could havecontinued partially even though the temperatureof the containment vessel dropped.
In addition, it is estimated that under pre-cold
shutdown conditions, the dehumidifier forcontainment vessel atmosphere monitoring
could not have functioned due to the loss ofcooling sources, and since sample gas
temperature and humidity exceeded service
conditions, it deviated from the measurements.
After cold shutdown, however, sample gas
dehumidifier function was recovered. It should
be remarked, however, that the reliability of theHydrogen concentration meter needs
investigation (page 220 of Main Text).

A method of monitoring Hydrogenconcentration is being developed
based on the experiences inFukushima Daiichi.

OthersMarch 11

The main administration office evacuated to theparking area that had been designated as anevacuation site, and conducted confirmation of
The safety of some
employee safety.
employees could not
Emergency response personnel then moved tobe confirmed.
the important anti-seismic building while other
employees evacuated to a field (page 136 of
Attachment 2).

(6) Lesson

It is required to conduct
Failure to directconfirmation of missing
evacuation to theemployees in addition to
designated place andrestoration works, which
confirm personnel
has an adverse impact
safetyon the restoration works.

No.

58

• There were provisions in the
manual for emergency events.
• Training was conducted.

5.4 Important lessons obtained from the analysis
As a result of the analysis, the following points were obtained as important lessons. It is
desirable that the contents of these lessons are also applied in other power plants as
preparations for large-scale accidents.
① Appropriate governance of the response headquarters at the power plant.
Important features required in the on-site headquarters are as follows:• An accurate understanding of the circumstances of the accident (plant parameters,
status of damage of equipment).
• Each team of the headquarters shall fulfill the assigned tasks as shared among theteams.
• The conductor of the headquarters shall accurately pick up the opinions/informationfrom each group and ensure that they are shared.
• Develop appropriate response strategy. (Example: making decisions on the recovery
plan priority, appropriate routing of cable laying)• For the implementation of individual response, create appropriate ad hoc measuresin line with the situation at hand, and establish a proper framework for
implementation. (Example: Establishing a reliable channel for communication withthe patrolling team for the contingency of a tsunami warning.)• Not only respond to the development of the event, but prepare proactive measures.
(Example: line configuration in preparation for the containment vessel vent.)② Establishment of a system to receive immediate assistance, supply of materials fromexternal organizations.
For the restoration works of the residual heat removal system, equipment andmaterials such as motors usable for the residual heat removal system pump and alarge amount of cables spanning 9 km were quickly procured from outside, and large
number of personnel, including workers skilled in cable laying, were dispatched tohelp.
These quick arrangements can be attributed to following factors.
• The power company is vertically integrated to handle power generation andtransmission, so the human resources for cable laying and equipments/materials
such as cables were all available in the same company, making rapid procurement
possible.
• The cooperating companies are stationed in the plant site, and a close relationshipwith them has been established on a day-to-day basis to facilitate cooperation in
emergency situations. To ensure quick procurement of materials and equipment,
development of the following is desirable:• Maintaining a list of suppliers for a variety of equipment.
• Secure a driver with a license for large vehicles for carrying large and heavyequipment (for receiving the supply of cargo from companies which are not allowed
to let their staff enter a nuclear disaster evacuation zone.)• Support by government agencies including transportation of heavy and large cargo
by SDF helicopters.
③ It is desirable to foster a culture of safety among all related personnel, including not
only TEPCO employees but also the workers of cooperating companies, for the59purpose of strong determination and a sense of mission to achieve convergence inthe event of an emergency, even in a hazardous environment such as high radiation
dosing from the nuclear disaster caused by the tsunami due to the aftershocks.
④ Seismic design proved effective.
As intended, equipment in the safety systems that have been installed withstate-of-the-art seismic design worked without failure, even in ground motion. In
addition, the equipment used for the conventional AM system (MUWC) also
withstood ground motion beyond the design standard by its own margin and kept
functioning without failure.
⑤ Maintenance of procedure and staff training in advance worked well.
Among other factors, the most notable ones which enabled a variety of smooth andswift responses were that procedure manuals were prepared in advance and all theoperating personnel and workers, being familiar with the procedures, responded
appropriately according to the procedures as prescribed in the manuals.
⑥ The importance of the back-up structure to allow the operating staff of the central
control room to concentrate on the operation of the reactor.
The operating personnel of the central control room received overall support from theplant so as to be able to concentrate on the operation of the reactor. This included
maintaining normal shifts, increasing the number of patrollers, dispatching liaisons forbetter communication, and centrally controlling contact with off-site entities by the
emergency headquarters. Successful convergence of the accident can be attributed
to these support systems.
⑦ Peripheral earthquake preparedness other than seismic design of facilities andequipment or emergency operating procedures was also effective.
The plant already had variety of earthquake preparations in place from the
Chuetsu-oki Earthquake, and these proved effective this time. Example: Fastening
and fixing loose furniture in the main control room and offices, preparing temporary
lighting and handheld microphones, etc.

60

6. Emergency response as seen from the viewpoint of the human factor
With respect to the emergency response at Fukushima Daini, some situations that actuallyoccurred were not described in the manual or handled in the usual training drills, and so thecapabilities of plant organizations and individuals to handle the situation were tested. In these
difficult circumstances, their response was generally adequate and under good leadership,
and it successfully prevented the spread of the accident, leading to convergence.
We have analyzed the background from the viewpoint of the human factor. Table 6-1 shows
the results of analysis by the m-SHEL model. We also made analysis based on a method ofanalyzing the resilience of the organization. The results are shown in Table 6-2.
In terms of human factors, there were considered to be two major factors that contributed tothe successful convergence of the accident: the appropriate management of the accident
response, and the effectiveness of the various measures that had been prepared in advance.
In order to ensure the effectiveness of management, it is necessary that the senior
management perform good leadership with sufficient knowledge, and the organization should
be well disciplined, which requires ongoing efforts to establish a good work environment undernormal circumstances.
Important areas that require advance preparation may be: establishment of an emergency
system (including an external support system), maintenance of manuals, cultivation of aculture of safety, education and training, stockpiling of food, and installation of a seismic
isolation building. These requirements also call for ongoing efforts under normal
circumstances.
Some fortunate circumstances were observed in this accident, such as a single line of theexternal power supply remaining online by chance, there being relatively insignificant tsunami
damage to some of the vital facilities, or accident convergence being achieved in a relatively
short time. However, in preparing for future accidents, we must assume that we cannot expect
these fortunate circumstances.
We also performed analysis focusing on the resilience of Fukushima Daini as an organization.
We identified the good practices of the organization from four perspectives and concluded
that the organization as a whole is well-balanced. Finding these good practices also indicatedthat the strength of the organization comes from ongoing efforts under normal circumstances(development of manuals and training). In addition, it is necessary that each and every
member of personnel hold a strong sense of mission for safety. This serves as the foundation
to support the strength of these organizations. We have been reminded once more that
fostering a culture of safety is truly important.

61

Table 6-1 Human factors that contributed to the convergence of the accidentManagement
 The pre- determined emergency system
clearly defined role assignment. Systemestablished as soon as the earthquake hit
and utilized effectively.
 Senior management exercised strong andunperturbed leadership when making
analysis for accurate instructions.
 Intent of instructions clearly understoodby all personnel through information
sharing.
 Action plans were prepared not only inresponse to actual event development but
in the sense of proactive strategy.

Software Procedures prepared in anticipation of themain condenser being unusable as a heatsink.
 Root contact was in place for mobilizing
emergency response personnel.
 Instructions were effective.
 Restoration team dispatched patrol teamafter determining evacuation proceduresin advance.
 A video conference system was available
with the head office and KashiwazakiKari-wa. Multiple communication
channels were available.

Hardware Important seismic isolation building
functioned.
 Power source remained functional.
 RCIC was available thanks to only minor
inundation by the tsunami.
 Radiation management equipment was
free of earthquake and tsunami damage,
and was secured.
 AM equipment was functional without
failure, even for ground motion beyond
the design intensity.

Environment
 Outside disturbance was minimal andplant was mostly able to handle thesituation at its discretion.

Live ware Sufficient knowledge to predict the
progress of events to plan effective
countermeasures.

 Earthquake occurred on a weekday
afternoon and the emergency response
system was smoothly established.
(Necessary personnel swiftly secured) Operators performed adequate
operations without mistakes.

 Sufficient stockpile of drinking water andfood was available.
 Emergency response headquarters able
to carry out operations at the importantseismic isolation building.
 A grip bar was available on the operation
panel of the central operation room for
operators to hold on to.

 A system to receive quick support fromoff- site was in place. Procurement ofequipment and materials was reasonably
quick.

 Cabinets were fastened and secured toprevent tripping.

 A system was established so that
operators in the central control room
could concentrate on the operation ofreactor.

 Instruments remained functional, so thesituation could be confirmed.
 Proper lighting and communications weremaintained, so the work environment was
not significantly adverse.
 Prospect of accident convergence
foreseen in relatively short time.

62

 In the event of an emergency, allpersonnel maintained a strong sense of
mission to achieve convergence even in ahazardous environment. (Suchpsychological culture of safety was
fostered at the plant.)
 All personnel were well educated andtrained to execute duties properly inaccordance with instructions.
 Some TEPCO employees had
professional expertise in driving large
vehicles.

Table 6-2 Analysis of the resilience of Fukushima Daini
Responding Equipment still in operating condition after theearthquake could be confirmed at the central
operating room.

Monitoring Operation of equipment was confirmed by the lamps
in the central operating room.

Anticipating Power source recovered quickly for the worst
contingency of total loss of external power.

 Site patrol was conducted to check damage toequipment.

 Recovery procedures were prepared based on plantsituation and site patrol findings.

 The main parameters of the plant were continuously
monitored at the headquarters.

 Prioritized recovery plan of units from the changes inparameter and executed in sequence.

 Information from each group was visually displayedon a white board to ensure sharing among all staff.

 Confirmed function of MUWC while RCIC was inoperation.

 Based on the experience of the Chuetsu-oki
earthquake, a variety of preparations were in place:
installation of the important seismic isolation building,a grip bar on the operating panel of the central
operation room, and securing of cabinets to prevent
tripping.

 A patrol team was dispatched to the scene only after
evacuation procedures were established.

 A system was in place to receive quick support fromoff- site.

 Recovery procedures were quickly prepared and eachteam began work after confirming tasks.

 Smooth communication between each group andheadquarters for close instructions and progress
reports maintained through frequent and mutual
reports, advice and consultations.

 Procurement of equipment and material was arranged
as far in advance as possible.

 Dry well spray was conducted to cool the containment
vessel.

 The integrity of the instruments was confirmed bymonitoring the continuity of parameter variations.

 After examination based on the manual, a temporary
cooling system configuration of RPV and S/C using
one unit of RHR was devised as the operation to be
applied.

 Personnel with operator experience were dispatchedto the central operating room so that operating
personnel could concentrate on operating the reactor.
 An emergency system was immediately establishedafter the earthquake.
 A patrol team was quickly organized and dispatchedto check conditions at site.

 Early arrangements for procurement of equipment
and support of workers were initiated.

 Daily rations of water and food were adjusted forpossible prolongation of the situation.
 Assuming the worst, containment vessel vent was
prepared in advance.

Resilience: Capability of organization to ensure continuous success in the ever-changing circumstances.
 Responding:

Response to incident

 Monitoring:

Monitoring of development of incident

 Anticipating:

Anticipation of threats and opportunities Learning:

Learning from past success and failure

63

Learning A video conference system was available with thehead office and Kashiwazaki-Kariwa. Multiple
communication channels were available.

7. Lessons
Fukushima Daini’s accident response includes a variety of best practices in many aspects
from which we can learn valuable lessons. In addition, since the impact of the tsunami at
Fukushima Daini was limited compared with Fukushima Daiichi, the parameters and functionof equipment were not lost like Fukushima Daiichi and the plant did not suffer such extreme
conditions of high pollution or high-dose exposure. Therefore, the lessons taken therefrom
should be applicable to many other power plants as practical lessons.
We compiled this section by combining these lessons and the lessons that were foundthrough the analysis in Section 5. We hope that our findings will be used in the future as
reference material when introducing accident countermeasures.
7.1 Organization, management, communication• The basic aspects of accident response are 1. an adequate grasp of the situation, 2.
planning immediate action plans and a complete restoration schedule in the longer term,
3. procuring materials and equipment required for the restoration, 4. executing the planand schedule while monitoring the situation. In addition, it is also important to allocate
the manpower necessary for the purpose and give appropriate instructions in a timely
manner when sharing information.
• The results of the analysis of the human factor indicate that management is criticallyimportant in the event of an accident and suggest that the education and training of thesenior management of the plant is especially important.
• Emergency group organization and role assignment were determined in advance,
enabling smooth implementation of accident response. Each team was able to fulfill theirrespective roles in a flexible manner through appropriate and frequent reporting,informing and consultation. One of the most important factors in accident response is thedevelopment of a personnel system and the assignment of human resources.
• An experienced operator was dispatched to the central control room to serve as a
dedicated liaison in order to convey a variety of information to headquarters or deliver
instructions from the Headquarters. As a result, operators could concentrate on theoperation of the reactor. At the same time, the Headquarters built a strong support
network for the staff by creating a good work environment, including centralizing all
contact with the outside including the head office, dispatching patrollers to grasp thesituation, and maintaining normal work shifts so that operators could take rest as
appropriate from time to time. It is imperative to establish a system that allows operators
to concentrate on the operation.
• All the planning of countermeasures was performed by the plant personnel without
resorting to the assistance of the plant manufacturers. When determining the priority of
the restoration, the first and foremost factor was the common and shared determinationof all the personnel to avoid the containment vent. Also, while the management does notaddress such a system, the circular loop system for cooling organized after the
restoration of the seawater system was a practical way to apply know-how. All thesegood practices seem to be attributable to the usual day-to-day efforts for education andtraining at the plant, which resulted in the improvement of the knowledge of plant
personnel. Under current circumstances where new plants are very seldom constructed,
the necessary field of knowledge for plant personnel is safety-related knowledge. It is
hoped that further efforts will be made to improve the knowledge of plant personnel,
such as accident mitigation through education on the concept of defense in depth.
• Dry well spray, which may have adverse effects upon the equipment in containment
vessels, is prescribed in the manual. Therefore, the plant manager decided to carry it at
his discretion. Rather than giving priority to preserving the asset value of the equipment,
he made this decision based on the idea of safety first in order to ensure the integrity of64

the containment vessel and hold the execution of containment vent down as far as
possible to avoid releasing radioactive materials into the environment. This shows thatthe culture of safety has firmly taken root there. It is necessary to make daily efforts tofoster this culture among all the personnel in the organization, from the plant manager
down to the workers.
• The required equipment was supplied in a short time thanks to the external assistancewhich contributed to the early recovery. It is necessary to establish a quick support
system at the head office in an emergency. The agreements for support andco-operation in case of emergency that had been executed with support companies andmanufacturers were effective. It is desirable to develop a system for the procurement ofmaterials and equipment at the time of an accident. It may be a good idea to establish
cooperation agreements between power companies to enable the lending or quick
supply of equipment and materials.
• The restoration work was carried out through joint efforts together with the work force ofcooperating companies, which made the early recovery of equipment possible,
contributing to the early convergence of the accident. Subcontractors should be included
when accident response preparations are carried out in order to enhance cooperative
relationships through training and through fostering a sense ownership.
• Early recovery of external power was achieved with the help of the engineering division.
Such support from within the same company was an advantage in terms of the response
capabilities. When assuming a situation in a large-scale disaster that requires
inter-departmental cooperation within the company, it is desirable to build up a system
and mutual understanding for internal cooperation through training etc.
7.2 Advance preparation (equipment, manual, training)• Because the accident occurred on a weekday afternoon, mobilizing the necessary
manpower was easy. But if it had been on a holiday or at night, mobilizing the large
number of necessary staff would have taken a long time. In this regard, it is necessary tokeep adequate, necessary manpower for initial response stationed at the site, and a
response plan shall be prepared based on a realistic scenario in which the workforce
gathers gradually over a period of time. For this reason, mobilization drills shall be
exercised from time to time to assess the number of personnel to gather and the time atwhich they should convene. Such advance preparation shall be conducted not only for
TEPCO personnel but also for the personnel of partner companies.
• Emergency headquarters were affected by the earthquake and tsunami, and theyfunctioned effectively. At the important seismic isolation building, power was lost
because the power distribution panel was flooded. An emergency gas turbine generator
was in place but it did not work due to the impact of the tsunami. It is desirable toenhance the reliability of the power source through higher vibration resistance design orwatertight equipment design. We can also see that there was the possibility of achieving
restoration of the gas turbine generator much earlier if its situation had been checked
immediately. On-site surveillance is truly important.
• In the headquarters, plant parameters and other necessary information was displayedon a large display panel and shared by everyone at the headquarters. Thus, planning ofeffective measures was ensured, and the purpose/intent of instructions was clearly
identified. During the power blackout, information and instructions were posted on thewhiteboard. In addition, the power plant has a video conference system for sharing
information which is connected with the head office and three power plants. This helped
get a swift supply of motors for the seawater pump from Kashiwazaki-Kariwa, resulting
in a quick recovery. All these cases indicate that the headquarters should establish aneffective system to share information between the parties concerned.

65• Since AM equipment and its manuals, which prescribe the use of MUWC, were in place,it was possible to utilize these functions to suppress the expansion of the accident.
Training carried out ordinarily was also effective. In the future, a variety of equipment tocombat severe accidents shall be prepared in addition to the AM equipment. Training forproficiency in the use of these facilities will be necessary, and feedback of the training
results shall also be implemented for continuous improvement and to achieve a quicker
and more accurate response.
• Special expertise and tools are required in cable laying works. To transport materials
and equipment, TEPCO employees were forced to drive large vehicles because ofradioactive material fallout. Securing such personnel with special skills, expertise, andtools in advance, for the assumption of various situations that may occur during an
accident, is desirable and shall be properly prepared. In addition, the cooperation of the
SDF is essential, including the delivery of materials and equipment in the case of acomplex accident created by a catastrophic situation outside due to earthquakes andtsunamis. In the future, these issues should be addressed in the study of the entire
disaster prevention system.
• The ample amount of food prepared in advance for emergencies was utilized effectively
as short-term rations. However, by allocating the stock to all the workforce of theexternal support teams and staff of cooperative enterprises, the situation became direand difficult from the second day. It is not practical to keep stock to provide food andwater to people in the magnitude of 2,000 over a long period of time. A practical
approach may be to keep a stock of food and water for a few days and prepare a system
to secure the supply and transportation measures thereafter. It may be a sensible idea toimplement cooperation agreements with nearby power plants and adjacent powercompanies to share and lend their stock of food and water in an emergency.
• The grip bar attached to the control panel of the main control room was useful during theearthquake tremors. Anti-trip precaution measures taken for the cabinet and furniture in
the office were effective in preventing human injury. These earthquake tremor
countermeasures are desirable.
7.3 Initial response in the accident• At Fukushima Daini, the lamp display in the central control room allowed loss of function
to be confirmed and known at an early stage. In addition, the status of the plant and thereactor core could be observed in real time by monitoring the key parameters, which
helped in the appropriate maneuvers of the plant. However, it is desirable to prepare
appropriate measures, such as spare batteries, to collect parameters and otherinformation when power has been lost. Specifically, vital parameters such as reactor
pressure, reactor water level, primary coolant temperature, containment pressure, andcontainment temperature should be made available even in the most severe situation.
• In a difficult situation where communication was unreliable, after setting up evacuation
procedures, patrollers were dispatched to walk down to the site in order to determine if
the damaged equipment could be recovered quickly. The findings of the patrollers madeit possible to accurately grasp the status of the equipment, which in turn made it possible
to determine a recovery plan in line with the actual situation. It is important to grasp thesituation as early as possible while ensuring safety. How to check the status in difficult
situations such as loss of external power supply, for example, shall be discussed andappropriate measures shall be prepared in advance. Assuming a walk down patrol to thesite when power and lighting are lost may require temporary lighting.

66• Countermeasures are considered strategically based on the idea of defense in depth,
such as a preparation for the containment vent, for example, which is a proactive
countermeasure in planning rather than a reactive action responding to the progress of
events. The external power supply was received via one series of transmission systems
after the earthquake. However, in anticipation of its failure and loss, the other series
were restored in the most urgent manner. The execution of effective response measures
based on good foresight is desirable.
• To ensure the safety of patrollers, a contact liaison was stationed in the site with a PHS
handset connected at all times to ensure contact, who would go down to the patrollers todeliver evacuation instructions if a tsunami warning was issued. It was reported that at
Fukushima Daiichi, they experienced difficulty in the use of transceivers because of
signal interference when they tried to use transceivers instead of the PHS, which had
stopped functioning. If the transceivers had frequency bands which were different toeach other, they could have been used as an effective means of communication. Also,
loudspeakers and megaphones may be convenient and effective tools to eliminate thenecessity of a messenger running to distant locations of the site.
7.4 Additional measures• One of the major factors that contributed to the early convergence of the accident at
Fukushima Daini is the availability of an online external power supply and that thestarting transformer was not affected by the tsunami either. Ingenious effort should be
exerted to come up with all possible measures to minimize the possibility that everything
will be lost due to an external event such as an earthquake or tsunami. With respect tothe external power supply, every power company is trying to improve its reliability under
the guidance of the national government by improving the seismic design or installing
additional transmission lines so as to enable interchange of power between units. It is
important to be prepared for extreme external events such as tsunami or violent winds inorder to avoid the total loss of external power.
• Depending on its mode of usage, the emergency power vehicle will use up its fuel withina few hours. Therefore, it is necessary to continuously monitor the fuel to replenish it in atimely manner. When using the temporary equipment, you should confirm in advanceappropriate measures for the procurement of fuel and utility in anticipation of using it fora long time.

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8. Conclusion
First of all, we would like to express our deepest appreciation to all the TEPCO personnel who
participated in the compilation of this report on the accident response at Fukushima Daini bygiving us details in various ways.
The report issued by the Accident Investigation Board of the Government in July has highregard for Fukushima Daini for its appropriate accident response, but is critical of that of
Fukushima Daiichi.
However, the impact of the earthquake and tsunami at Fukushima Daini was smaller than thatof Fukushima Daiichi, and as a result, an external power source was available at Daini. AM
equipment and manuals were also available at Daini, which was activated by external power,
and were used to bring the plant to convergence.
As we summarized as a lesson, the accident response at Fukushima Daini shows us anumber of excellent ways to cope, such as: organization management, appropriate response
by well-trained operators, effective use of equipment prepared in advance, and support fromoutside materials.
It may be meaningless to apply hypothetical hindsight to reviewing past incidents, but if somepart of the power source had remained available, then there might have been the possibility
that they could lead the plant to convergence in the same manner as Fukushima Daini,
although the hard fact is that they lost all power panels due to the tsunami flooding, and theaccident expanded.
Currently, stress tests are conducted on all nuclear power plants in Japan to strengthen all of
the vulnerable points. For effective improvement, it is important to address not only the aspectof hardware, but also of software. In this respect, a variety of valuable information derived
from the response to the accident at Fukushima Daini should be useful as reference material
for consideration. We hope that this report will be used in Japan and around the world.
As for enhancing safety measures at nuclear power plants in the future, it has been
determined that the Japan Nuclear Safety Institute, which was established in November, willtake the helm and leadership. We hope the results of this study will be used by this neworganization and contribute to nuclear power plant safety in Japan.
We prepared this report focusing on lessons from the accident response at Fukushima Daini,but there are two more nuclear power plants which were led to accident convergence despite
the impact of the earthquake and tsunami: Onagawa Nuclear Power Station of Tohoku Electric
and Tokai Daini Power Station of JAPC. We await future analysis and validation of theiraccident response to find lessons, and we expect that the new organization will address thesetasks.

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Attachment
Recommended Actions for the Emergency Response by Equipments/Materials
Reinforcement
This report provided a wide range of lessons learned in terms of the organization,
management structures and preparation of small equipment/materials. Among them, this
attachment summarizes specific recommendations for consideration in the chart below,
including an arrangement of equipment/materials for emergency response, which may beeffective for the same incident.
Please note that the following is based on the measures taken at Fukushima Daini and keep
in mind that plenty of room is left for other kinds of possible efforts.
Operation
Item(1) Installing a bar at
the central operating
panel(2) Fixing cabinets inthe central operatingroom(3) Handheld
microphone(4) On-site surveillancecamera (to grasp thesituation visually)(5) Support staff for thecentral operating room
Recovery efforts
Item(1) Secure storage ofequipment structural
drawings(2) List of suppliers ofnecessaryequipment/materials(3) Prior consideration
for transportation ofequipment/materials forrecovery

Details
Operators can grip the bar and stand by, keeping low, for thereactor scram operation after the earthquake. In addition, suchstand-by position should be included in training to ensure that
operators can keep low in the event of the earthquake.
Fix cabinets and other equipments to prevent them from falling so
as not to hurt operators or adversely affect the environment at thecentral operating room. Also fix meeting tables and whiteboard,etc.
Handheld microphones are effective to make sure directions fromthe shift supervisor can be clearly communicated in a situation
with loud noise due to a fire alarm malfunction during theearthquake. This should be included in training.
The surveillance camera allowed the central operating room to
see the tsunami onslaught. Be sure that the surveillance footage
can be checked at the central operating room, which will beeffective in observing the situation.
Prepare to dispatch support staff to the central operating room asa procedure during an accident.

Details
Equipment structural drawings required for considering recovery
actions could not taken from the main office building due todamage, and digital libraries were not available due to theblackout. Make preparations so that they can be used in the eventof an earthquake, fire, or blackout. (Strengthen the seismic
resistance of the document storage room, entrance, and rack, andstore documents in separate places assuming that fire will spreadto the main office building)
Seawater pump motors were procured from outside the plant
because they were flooded by the tsunami seawater. Preparing
the list of necessary equipment/material suppliers in advance iseffective for quick procurement.
The major earthquake caused confusion in transportation(blockages of national roads, insufficient detours, and traffic jams)
and transport companies refused to deliver to the evacuation
area. Consequently, TEPCO employees had to deliver materials
on their own. However, pick-up meetings were difficult due tomobile phones being disconnected. Therefore, prior considerationfor equipment/material transportation is required assuming such69

conditions.

(4) Securing heavymachinery operators

Since transport companies refused to deliver to the evacuationarea, directly managed transport was required. Thus, drivers forheavy trucks should be secured (a list of such drivers; training
personnel with licenses for heavy vehicles).
(5) Securing personnel TEPCO employees not only drove heavy trucks but also operated
with special skills
cranes and connected cables on their own. Secure employeeswith the capability to handle such operations in the event of an
accident.
(6) Preparing temporary For recovery, small equipment such as temporary lighting andhandheld microphones were useful. Transceivers might belighting, handheld
effective as a means of communication. Secure a certain quantity
microphones, andof such equipment/materials.
transceivers
Support from cooperating companies was essential for recovery.
(7) Prior arrangement
Consider strengthening the following approaches to prepare forof support fromcooperating companies an accident.
• Conclude a contract on emergencies with on-site cooperatingcompanies• Recovery training involving on-site cooperating companies• Prior consideration for arranging support staff from cooperating(8) Measures forunavailability ofcooperating company
buildings due to theearthquake(9) Strengthening
medical/health carecompanies in an emergency
A cooperating company’s building could not be used for a while
due to earthquake damage. Check items in that building which areessential for recovery but may be unavailable due to damage.

Because many staff work and live in small places, strengthen
medical and health care such as health management andcontinuous physical support for the late-onset de-conditioning due
to stress.

Information sharing method
Item
Details(1) Plant parameter
Indicate plant parameters at the emergency headquarters toindications at theunderstand plant conditions.
emergency
headquarters
Simultaneous video conference among the head office, other(2) Video conference
TEPCO plants, and the Tokyo branch to make immediate support
system with the headpossible.
officeLogistics
Item(1) Food and waterstock(2) Fuel procurement

Details
In reality, a larger number of the necessary employees andcooperating company staff were engaged in recovery efforts
under the predetermined emergency procedure. Based on thisachievement, stock the proper volume of food and water andconsider the method of procurement from outside suppliers.
Ensure a method to procure fuel for power supply cars in theevent of a major earthquake.

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